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# At a blind taste competition a contestant is offered 3 cups of each of

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At a blind taste competition a contestant is offered 3 cups of each of  [#permalink]

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Updated on: 06 Feb 2019, 23:35
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At a blind taste competition a contestant is offered 3 cups of each of the 3 samples of tea in a random arrangement of 9 marked cups. If each contestant tastes 4 different cups of tea, what is the probability that a contestant does not taste all of the samples?

A. $$\frac{1}{12}$$

B. $$\frac{5}{14}$$

C. $$\frac{4}{9}$$

D. $$\frac{1}{2}$$

E. $$\frac{2}{3}$$

Originally posted by Economist on 14 Nov 2009, 07:34.
Last edited by Bunuel on 06 Feb 2019, 23:35, edited 3 times in total.
Updated.
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Re: At a blind taste competition a contestant is offered 3 cups of each of  [#permalink]

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14 Nov 2009, 08:06
41
31
Economist wrote:
At a blind taste competition a contestant is offered 3 cups of each of the 3 samples of tea in a random arrangement of 9 marked cups. If each contestant tastes 4 different cups of tea, what is the probability that a contestant does not taste all of the samples?

# $$\frac{1}{12}$$
# $$\frac{5}{14}$$
# $$\frac{4}{9}$$
# $$\frac{1}{2}$$
# $$\frac{2}{3}$$

And the good one again. +1 to Economist.

"The probability that a contestant does not taste all of the samples" means that contestant tastes only 2 samples of tea (one sample is not possible as contestant tastes 4 cups>3 of each kind).

$$\frac{C^2_3*C^4_6}{C^4_9}=\frac{5}{14}$$.

$$C^2_3$$ - # of ways to choose which 2 samples will be tasted;
$$C^4_6$$ - # of ways to choose 4 cups out of 6 cups of two samples (2 samples*3 cups each = 6 cups);
$$C^4_9$$ - total # of ways to choose 4 cups out of 9.

Another way:

Calculate the probability of opposite event and subtract this value from 1.

Opposite event is that contestant will taste ALL 3 samples, so contestant should taste 2 cups of one sample and 1 cup from each of 2 other samples (2-1-1).

$$C^1_3$$ - # of ways to choose the sample which will provide with 2 cups;
$$C^2_3$$ - # of ways to chose these 2 cups from the chosen sample;
$$C^1_3$$ - # of ways to chose 1 cup out of 3 from second sample;
$$C^1_3$$ - # of ways to chose 1 cup out of 3 from third sample;
$$C^4_9$$ - total # of ways to choose 4 cups out of 9.

$$P=1-\frac{C^1_3*C^2_3*C^1_3*C^1_3}{C^4_9}=1-\frac{9}{14}=\frac{5}{14}$$.

Hope it's clear.
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Re: At a blind taste competition a contestant is offered 3 cups of each of  [#permalink]

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06 Feb 2011, 08:18
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i solved the question as follows. i hope my approach is correct.

let's consider that the contestant tasted all 3 flavors.
the first cup can be selected from any 9 cups. P = $$\frac{9}{9}$$
the second cup can be selected from 6 (other 2 flavors) of the remaining 8 cups. P = $$\frac{6}{8}$$
the third cup can be selected from 3 (flavor not tested yet) of the remaining 7 cups. P = $$\frac{3}{7}$$
the fourth cup can be selected from any of the remaining 6 cups. P = $$\frac{6}{6}$$

there are $$2$$ ways in which second & third cup can be tested {AB, BA}. first & fourth cup already have probability 1.

probability that the contestant tasted all flavors = $$\frac{9}{9}*\frac{6}{8}*\frac{3}{7}*\frac{6}{6}*2 = \frac{9}{14}$$

required probability = $$1 - \frac{9}{14} = \frac{5}{14}$$

##### General Discussion
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Re: At a blind taste competition a contestant is offered 3 cups of each of  [#permalink]

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15 Nov 2009, 04:16
8
5
I got B: 5/14 as well, although using a different approach.

Number of ways to choose 4 cups to drink from: 9C4

Since the contestant must drink 4 cups of tea, and there are only 3 cups of each tea, the contestant MUST drink at least two different samples.

Number of ways to choose which two samples the contestant drinks (since he can't drink all 3): 3C2

Three cases:

a) 3 Cups of Sample 1, 1 Cup of Sample 2: 3C3 * 3C1
b) 2 Cups of Sample 1, 2 Cups of Sample 2: 3C2 * 3C2
c) 1 Cup of Sample 1, 3 Cups of Sample 3: 3C1 * 3C3

Therefore,

$$P = \frac{3C2(3C3*3C1 + 3C2*3C2 + 3C1*3C3)}{9C4}$$

$$P = \frac{3(1*3 + 3*3 + 3*1)}{\frac{9*8*7*6}{4*3*2*1}}$$

$$P = \frac{45}{{9*2*7}}$$

$$P = \frac{5}{14}$$
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Re: At a blind taste competition a contestant is offered 3 cups of each of  [#permalink]

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18 Mar 2016, 00:58
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1
The probability of tasting all 3 cups is

One cup from pool A ($$\frac{3}{9}$$) x One cup from pool B ($$\frac{3}{8}$$) x One cup from pool C ($$\frac{3}{7}$$)

Since the contestant has to taste 4 cups, one possibility is picking second cup from pool A, so the probability is $$\frac{2}{6}$$

The probability of tasting in order of ABCA is $$\frac{3}{9} * \frac{3}{8} * \frac{3}{7} * \frac{2}{6}$$ ..... (1)

In how many ways can the contestant taste ABCA cups = $$\frac{4!}{2!}$$ = 4 x 3 ....... (2)

The combinations ABCB & ABCC are also possible (along with ABCA) = 3 combinations ..... (3)

Since the choice of "a specific cup" from "a pool" doesn't matter here, we need NOT account for $$A_1A_2A_3, A_1A_3A_2,$$ ... etc. combinations

So Probability of tasting all three cups is = (1) * (2) * (3)

= $$\frac{3}{9} * \frac{3}{8} * \frac{3}{7} * \frac{2}{6} * 4 *3 *3$$

=$$\frac{9}{14}$$

Hence, Probability of NOT tasting all three cups = $$1- \frac{9}{14} = \frac{5}{14}$$
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Re: At a blind taste competition a contestant is offered 3 cups of each of  [#permalink]

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12 Jan 2015, 08:47
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3
I solved it in a way that I think is more direct:
I get the probability that each cup is not a specific type of tea (type A):
1st cup, Probability it is not type A = 3/9
2nd cup, Probability it is not type A = 3/8, since we only have 8 cups left, and 3 of them are type A
3rd cup, Probability it is not type A = 3/7
4th cup, Probability it is not type A = 3/6
We do the same for types B and C (multiply by 3)
So : 3/9 * 3/8 * 3/7 * 3/6 * 3 = 5/14
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Re: At a blind taste competition a contestant is offered 3 cups of each of  [#permalink]

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17 Jun 2019, 06:13
4
dimitri92 wrote:

i solved the question as follows. i hope my approach is correct.

let's consider that the contestant tasted all 3 flavors.
the first cup can be selected from any 9 cups. P = $$\frac{9}{9}$$
the second cup can be selected from 6 (other 2 flavors) of the remaining 8 cups. P = $$\frac{6}{8}$$
the third cup can be selected from 3 (flavor not tested yet) of the remaining 7 cups. P = $$\frac{3}{7}$$
the fourth cup can be selected from any of the remaining 6 cups. P = $$\frac{6}{6}$$

there are $$2$$ ways in which second & third cup can be tested {AB, BA}. first & fourth cup already have probability 1.

probability that the contestant tasted all flavors = $$\frac{9}{9}*\frac{6}{8}*\frac{3}{7}*\frac{6}{6}*2 = \frac{9}{14}$$

required probability = $$1 - \frac{9}{14} = \frac{5}{14}$$

I am having issues with the above, especially this line
there are $$2$$ ways in which second & third cup can be tested {AB, BA}. first & fourth cup already have probability 1.

in the 2nd fraction, 6/8, you already considered that either the 2nd or 3rd group can be considered. Why still a need for x2?
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Re: At a blind taste competition a contestant is offered 3 cups of each of  [#permalink]

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15 Aug 2010, 18:43
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1
It should be 1-(3*3C2*3C1*3C1/9C4)
= 1-9/14 = 5/14

Now why is your approach wrong ?
E.g: in how many ways 2 objects can be selected from a set of 3.
We know it is 3C2
As per the approach you took above it should be equal to; 3C1*2C1 != 3C2.

Hope it helps.
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Re: At a blind taste competition a contestant is offered 3 cups of each of  [#permalink]

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25 Sep 2017, 11:15
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DanceWithFire wrote:
cledgard wrote:
I solved it in a way that I think is more direct:
I get the probability that each cup is not a specific type of tea (type A):
1st cup, Probability it is not type A = 3/9
2nd cup, Probability it is not type A = 3/8, since we only have 8 cups left, and 3 of them are type A
3rd cup, Probability it is not type A = 3/7
4th cup, Probability it is not type A = 3/6
We do the same for types B and C (multiply by 3)
So : 3/9 * 3/8 * 3/7 * 3/6 * 3 = 5/14

1st cup : 3/9 is actually the probability that it's type A; Probability that it's not would be 6/9

Interesting way to approach the problem, though.

You are right, I made a mistake when I wrote it no the forum. The correct approach is the following:
I get the probability that each cup is not a specific type of tea (type A):
1st cup, Probability it is not type A = 6/9
2nd cup, Probability it is not type A = 5/8, since we only have 8 cups left, and 3 of them are type A
3rd cup, Probability it is not type A =4/7
4th cup, Probability it is not type A = 3/6
We do the same for types B and C (multiply by 3)
So : 6/9 * 5/8 * 4/7 * 3/6 * 3 = 5/14
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Re: At a blind taste competition a contestant is offered 3 cups of each of  [#permalink]

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15 Aug 2010, 19:03
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We want to select 2 cups of tea which are of similar type and the rest 2 cups which each are of different type ;
hence the terms 3C2 * 3C1* 3C1
Now you should multiply it by 3 because ; out of the 3 tea types , you may select the tea type which is in 2 cups, in 3 ways.

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Re: At a blind taste competition a contestant is offered 3 cups of each of  [#permalink]

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09 Mar 2013, 22:37
2
Hi,
Let me try..
mainhoon, you are going with the logic that you select 1 cup from each sample in 3c1 x 3c1 x 3c1 ways and 1 remaining cup from 6 cups in 6c1 ways rite!
I guess the flaw with your approach is that this 6c1 is the probablity of selecting 1 item from 6 DIFFERENT items (r items from n different items is nCr)
Im this case the 6 items left are not different! They are XX,YY,ZZ types right! so you just cant use the 6c1 fomula!
This is the formula : The number of ways of choosing r objects from p objects of one kind, q objects of second kind, and so on is the coefficient of x^r in the expansion

hope it helps!

mainhoon wrote:
Yes I can see that clearly I am ending up with more combinations than necessary. I was thinking if there is way to factor out those repeats the way I am doing it. I see your point in the simple example. However when I think of this, I am thinking of a 3x3 matrix where I have to make sure I get one from each row and the 4th can come from anywhere - that is the same thing as saying 2 from a row and 1 each from the remaining 2 (your and correct approach). My count differs from yours by a factor of 2 (I am 162 and you are 81). How can I rationalize this?
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Re: At a blind taste competition a contestant is offered 3 cups of each of  [#permalink]

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15 Feb 2018, 05:47
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To choose 2 types of sample out of 3, we get 3c2
We then have 6 cups and to choose 4 cups out of that we get 6c4.
Hence, 3c2 * 6c4
The total ways of selecting 4 cups out of the total 9 is 9c4.
Final ans is (3c2 * 6c4) / 9c4

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Re: At a blind taste competition a contestant is offered 3 cups of each of  [#permalink]

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06 Mar 2013, 02:32
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tosattam wrote:
Not sure if my channel of thought is flawed to start with, but when it is said that it's a 'blind' taste competition, I am considering repetitions. As the contestant does not know which of the 9 cups he/she had picked up the first time, the same can possibly be repeated in the second turn and so on until the fourth.
That gives a complete different perspective to the problem.
Where am I going wrong here?

A blind taste simply means that a contestant doesn't know which samples he/she is offered to taste.
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Re: At a blind taste competition a contestant is offered 3 cups of each of  [#permalink]

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06 May 2017, 10:22
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cledgard wrote:
I solved it in a way that I think is more direct:
I get the probability that each cup is not a specific type of tea (type A):
1st cup, Probability it is not type A = 3/9
2nd cup, Probability it is not type A = 3/8, since we only have 8 cups left, and 3 of them are type A
3rd cup, Probability it is not type A = 3/7
4th cup, Probability it is not type A = 3/6
We do the same for types B and C (multiply by 3)
So : 3/9 * 3/8 * 3/7 * 3/6 * 3 = 5/14

1st cup : 3/9 is actually the probability that it's type A; Probability that it's not would be 6/9

Interesting way to approach the problem, though.
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Re: At a blind taste competition a contestant is offered 3 cups of each of  [#permalink]

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05 Jun 2019, 22:21
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Although this approach may not be great, I used the elimination method after finding total possible ways of selecting 4 cups out of 9 = 4C9=112.

As I was not able to come up with the exact way to calculate the ways to select 4 cups of 2 samples...i checked for denominators being divisible by 112, as no answer choice can be correct if the denominator isn't a factor of 112. I was left with 1/2 and 5/14 as a potential answer choice, and by gut feeling the case looked to be of probability less than 50%(selecting 4 out of 9) hence excluded 1/2 and marked 5/14.

Though not best, such methods may come handy as a guessing strategy i feel.
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At a blind taste competition a contestant is offered 3 cups of each of  [#permalink]

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05 Jul 2019, 10:15
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Economist wrote:
At a blind taste competition a contestant is offered 3 cups of each of the 3 samples of tea in a random arrangement of 9 marked cups. If each contestant tastes 4 different cups of tea, what is the probability that a contestant does not taste all of the samples?

A. $$\frac{1}{12}$$

B. $$\frac{5}{14}$$

C. $$\frac{4}{9}$$

D. $$\frac{1}{2}$$

E. $$\frac{2}{3}$$

Really good problem. Let's break it down.

-- Does order matter? No. (i.e. Are we selecting or arranging? Problem says "random arrangement," this means selecting/combinations; all 3 cups of A are the same)
-- Is there replacement? No, unless specifically stated assume there is no replacement.
-- Is each grouping of them the same? Yes, for the denominator total (fundamental counting principle) but No for the numerator (we need to find 4 cups with a certain condition). There are 2 possibilities, either 2 types of tea or 3 types of tea, we can't get 1 type of tea because there's 4 selections and only 3 cups of each type.
-- The easiest way to approach is to find P(2 teas) = 1 - P(3 teas). I made a chart using slot method:

Ways to choose first, second, third, any tea type (3 * 2 * 1 * 1) * Number of cup choices ($$\frac{3}{9} * \frac{6}{8} * \frac{3}{7} * \frac{6}{6}$$)

Step by step:
3 ways to choose 1st tea type * 3 cups out of 9 total
2 ways to choose 2nd tea type * 6 remaining cups out of 8 total
1 way to choose 3rd tea type * 3 remaining cups out of 7 total
1 way to choose ANY type * 6 remaining cups out of 6 total (anything can fulfil this requirement; we are asking for the way to choose ANY tea, rather than the way to choose one of the 3 types. Since we can choose any tea, we can choose any cup also)

After reducing fractions, we are left with 9/14. Usually GMAT problems on probability will have answers that add up to 1, so I would expect that as a trap answer. Since we found the P(3 types) and are looking for P(2 types) we need to do 1 - 9/14 = 5/14.

locklock wrote:
I am having issues with the above, especially this line
there are $$2$$ ways in which second & third cup can be tested {AB, BA}. first & fourth cup already have probability 1.

in the 2nd fraction, 6/8, you already considered that either the 2nd or 3rd group can be considered. Why still a need for x2?

locklock That solution is similar to mine, but the poster reasoned through it a bit differently. I think what he meant was that there's 2 distinct ways for the second/third slot to account for (Say you pick Tea A for first slot, you can get B or C for 2nd slot. If you got B, then the 3rd is A, but if you got A, then the third is B). That's why he multiplied by 2.

I would write it like this because it's more clear to me:

Ways to choose ANY tea, 2nd tea, 3rd tea, ANY tea (1 * 2 * 1 * 1) * Number of choose cup choices ( $$\frac{9}{9} * \frac{6}{8} * \frac{3}{7} * \frac{6}{6}$$)

Step by step:
1 way to choose ANY tea type * 9 cups out of 9 total
2 ways to choose 2nd tea type * 6 remaining cups out of 8 total
1 way to choose 3rd tea type * 3 remaining cups out of 7 total
1 way to choose ANY type * 6 remaining cups out of 6 total.

You can see that the difference is only where the factor of 3 goes, whether in the ways to choose or the choices, so it works out to be the same.

Does that make sense?
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Re: At a blind taste competition a contestant is offered 3 cups of each of  [#permalink]

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15 Aug 2010, 20:06
Yes I can see that clearly I am ending up with more combinations than necessary. I was thinking if there is way to factor out those repeats the way I am doing it. I see your point in the simple example. However when I think of this, I am thinking of a 3x3 matrix where I have to make sure I get one from each row and the 4th can come from anywhere - that is the same thing as saying 2 from a row and 1 each from the remaining 2 (your and correct approach). My count differs from yours by a factor of 2 (I am 162 and you are 81). How can I rationalize this?
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Re: At a blind taste competition a contestant is offered 3 cups of each of  [#permalink]

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05 Mar 2013, 09:23
Not sure if my channel of thought is flawed to start with, but when it is said that it's a 'blind' taste competition, I am considering repetitions. As the contestant does not know which of the 9 cups he/she had picked up the first time, the same can possibly be repeated in the second turn and so on until the fourth.
That gives a complete different perspective to the problem.
Where am I going wrong here?
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Re: At a blind taste competition a contestant is offered 3 cups of each of  [#permalink]

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07 Apr 2016, 07:09
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Is this an okay way to think about this problem?

In the case where we want to use the alternate solution (1-opposite), would it be okay to say the following:

The number of ways to taste all the cups would result from the following choices:

(A A) B C

- Of the 3 samples, choose 1 to be a double
- Of the 3 samples, choose 2 to be singles
- Given our choice for the double, choose 1 location of 3 possible to represent the double
- Given our choice for the singles, choose 2 locations of the 3 possible to represent the singles

Hence our total desired outcome would be: (3C1)(3C2)(3C1)(3C2) / (9C4) = 9/14.
Our answer, therefore, would be 1 - 9/14 = 5/14
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At a blind taste competition a contestant is offered 3 cups of each of  [#permalink]

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22 Feb 2019, 10:49
Can someone explain where I am going wrong?

This was my approach:
For the first cup: 9 options
For the second cup: 5 options
For the third cup: 4 options
For the fourth cup: 3 options

(9 * 5 * 4 * 3)/(9C4 * 3!)

I am using the 3! to remove the order
At a blind taste competition a contestant is offered 3 cups of each of   [#permalink] 22 Feb 2019, 10:49

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