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Schezwan restaurant offers 5 chicken, prawn, beef, vegetable & tofu

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Schezwan restaurant offers 5 chicken, prawn, beef, vegetable & tofu  [#permalink]

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New post 23 Sep 2018, 00:40
3
00:00
A
B
C
D
E

Difficulty:

  65% (hard)

Question Stats:

35% (01:23) correct 65% (01:36) wrong based on 49 sessions

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Schezwan restaurant offers 5 chicken, prawn, beef, vegetable & tofu entrees served with either garlic or chili sauce. In how many ways can 3 entrees be served if no entry is served more than once?

A. 10
B. 60
C. 80
D. 100
E. 120
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Re: Schezwan restaurant offers 5 chicken, prawn, beef, vegetable & tofu  [#permalink]

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New post 23 Sep 2018, 01:06
2
I would say it is a tricky question since it is ambiguous.
There are 2 sources of confusion:
1) Do we count chicken, prawn, beef, and chicken, beef, prawn as same or as a different way of serving? I guess we can conclude that in one way, so we will need divide by 3!
2) Do we serve a sauce on the entree? Can we order a garlic chicken and chili beef? So we need to multiply by 8? can we order chicken without sauce? We will need to multiply by 27. Do we get a sauce in Panda Express way, we will need to multiply by 2, 3 or 4 depends on whether we can reject both or take both.

Anyway, with all this in mind, we can calculate that we have 5*4*3=60/3! = 10 * 8 = 80
Since answer C
But if you will calculate an ordered permutation 60 and multiply by 2 Panda Express style, you will get incorrect 120
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Re: Schezwan restaurant offers 5 chicken, prawn, beef, vegetable & tofu  [#permalink]

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New post 23 Sep 2018, 05:32
Can someone help solve this question with a clear method?
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Re: Schezwan restaurant offers 5 chicken, prawn, beef, vegetable & tofu  [#permalink]

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New post 23 Sep 2018, 05:37
Hi,

I am really confused.

1> I first tried to answer assuming ordered permutation way and got 120.
2> If it is not ordered but rather a combination of 3 items (out of chicken/beef/prawn/veg/tofu) in one entry, then their should be 5C3 ways of combining them - 10 ways which then should be multiplied by 2 ways of adding sauce. So the answer was 20.

Can someone please clearly lay down the strategy if there are subtle nuances in the question?
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Re: Schezwan restaurant offers 5 chicken, prawn, beef, vegetable & tofu  [#permalink]

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New post 23 Sep 2018, 07:58
could anyone explain the solution please? I cannot reach 80 anyhow.
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Re: Schezwan restaurant offers 5 chicken, prawn, beef, vegetable & tofu  [#permalink]

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New post 23 Sep 2018, 08:17
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Top Contributor
PLUTO wrote:
Schezwan restaurant offers 5 chicken, prawn, beef, vegetable & tofu entrees served with either garlic or chili sauce. In how many ways can 3 entrees be served if no entry is served more than once?
Answer Options: -

A. 10
B. 60
C. 80
D. 100
E. 120


Take the task of creating a meal and break it into stages.

Stage 1: Select 3 entrees
Since the order in which we select the entrees does not matter, we can use combinations.
We can select 3 entrees from 5 entrees in 5C3 ways (10 ways)
So, we can complete stage 1 in 10 ways

If anyone is interested, we have a video (below) on calculating combinations (like 5C3) in your head

ASIDE: We now have our 3 entrees, but we don't have a sauce for each entree.

Stage 2: Choose a sauce for one of of the entrees
We have 2 choices (garlic or chili sauce), so we can complete stage 2 in 2 ways

Stage 3: Choose a sauce for another entree
We have 2 choices (garlic or chili sauce), so we can complete stage 3 in 2 ways

Stage 4: Choose a sauce for the last remaining entree
We have 2 choices (garlic or chili sauce), so we can complete stage 4 in 2 ways

By the Fundamental Counting Principle (FCP), we can complete all 4 stages (and thus create a meal) in (10)(2)(2)(2) ways (= 80 ways)

Answer: C

Note: the FCP can be used to solve the MAJORITY of counting questions on the GMAT. So, be sure to learn it.

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Re: Permutation & Combination question  [#permalink]

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New post 23 Sep 2018, 08:34
thank you GMATPrepNow
this is hard to conceive, probably i've never faced this type of question
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Re: Schezwan restaurant offers 5 chicken, prawn, beef, vegetable & tofu  [#permalink]

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New post 23 Sep 2018, 10:52
GMATPrepNow wrote:
PLUTO wrote:
Schezwan restaurant offers 5 chicken, prawn, beef, vegetable & tofu entrees served with either garlic or chili sauce. In how many ways can 3 entrees be served if no entry is served more than once?
Answer Options: -

A. 10
B. 60
C. 80
D. 100
E. 120


Take the task of creating a meal and break it into stages.

Stage 1: Select 3 entrees
Since the order in which we select the entrees does not matter, we can use combinations.
We can select 3 entrees from 5 entrees in 5C3 ways (10 ways)
So, we can complete stage 1 in 10 ways

If anyone is interested, we have a video (below) on calculating combinations (like 5C3) in your head

ASIDE: We now have our 3 entrees, but we don't have a sauce for each entree.

Stage 2: Choose a sauce for one of of the entrees
We have 2 choices (garlic or chili sauce), so we can complete stage 2 in 2 ways

Stage 3: Choose a sauce for another entree
We have 2 choices (garlic or chili sauce), so we can complete stage 3 in 2 ways

Stage 4: Choose a sauce for the last remaining entree
We have 2 choices (garlic or chili sauce), so we can complete stage 4 in 2 ways

By the Fundamental Counting Principle (FCP), we can complete all 4 stages (and thus create a meal) in (10)(2)(2)(2) ways (= 80 ways)

Answer: C

Note: the FCP can be used to solve the MAJORITY of counting questions on the GMAT. So, be sure to learn it.

RELATED VIDEOS




Why do you have so many stages? Why wouldn't it be just two stages? I thought of just 2, the entrees and the sauces. So it would be 20 in total, or 5C3 * 2.
Another way I thought of was if you cannot repeat an entree, there are 24 options (5*2 + 4*2 + 3*2).

Can you explain why both of these solutions are wrong?
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Re: Schezwan restaurant offers 5 chicken, prawn, beef, vegetable & tofu  [#permalink]

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New post 23 Sep 2018, 12:43
Top Contributor
RefError wrote:
Why do you have so many stages?


It helps to avoid errors :)

RefError wrote:
I thought of just 2, the entrees and the sauces. So it would be 20 in total, or 5C3 * 2.
Another way I thought of was if you cannot repeat an entree, there are 24 options (5*2 + 4*2 + 3*2).
Can you explain why both of these solutions are wrong?


What do your values stand for?

While my solution might LOOK longer than it needs to be, I don't write out every stage on my notepad. HOWEVER, I make it very clear to myself what each is occurring at each stage.
So, for example, in your 2-stage solution, 5C3 * 2, what does 5C3 represent and what does 2 represent?

Likewise, in your other solution, 5*2 + 4*2 + 3*2, what does each part represent?

Once you start articulating what each stage represents, your solutions will improve.

Cheers,
Brent
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Re: Schezwan restaurant offers 5 chicken, prawn, beef, vegetable & tofu  [#permalink]

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New post 23 Sep 2018, 12:44
Top Contributor
faltan wrote:
thank you GMATPrepNow
this is hard to conceive, probably i've never faced this type of question


It's a tricky question.
It's also poorly-worded.

Cheers,
Brent
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Re: Schezwan restaurant offers 5 chicken, prawn, beef, vegetable & tofu  [#permalink]

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New post 24 Sep 2018, 06:23
GMATPrepNow wrote:
RefError wrote:
Why do you have so many stages?


It helps to avoid errors :)

RefError wrote:
I thought of just 2, the entrees and the sauces. So it would be 20 in total, or 5C3 * 2.
Another way I thought of was if you cannot repeat an entree, there are 24 options (5*2 + 4*2 + 3*2).
Can you explain why both of these solutions are wrong?


What do your values stand for?

While my solution might LOOK longer than it needs to be, I don't write out every stage on my notepad. HOWEVER, I make it very clear to myself what each is occurring at each stage.
So, for example, in your 2-stage solution, 5C3 * 2, what does 5C3 represent and what does 2 represent?

Likewise, in your other solution, 5*2 + 4*2 + 3*2, what does each part represent?

Once you start articulating what each stage represents, your solutions will improve.

Cheers,
Brent


Okay, here you go...
1. Why do you have 4 stages rather than two? You have 4 stages for entree * sauce * sauce * sauce. Why? Why not two stages for Entrees and Sauces. With two stages you would do the exact same thing you did, but without the additional two stage. 5C3 (choose 3 entrees from five entrees) * 2 (sauces).
2. Why is it also not appropriate to calculate as Option 1 + Option 2 + Option 3? Option 1 = 5 entrees * 2 sauces. Option 2 = 4 entrees * 2 sauces. Option 3 = 3 entrees * 2 sauces.
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Re: Schezwan restaurant offers 5 chicken, prawn, beef, vegetable & tofu  [#permalink]

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New post 24 Sep 2018, 06:49
Top Contributor
RefError wrote:
1. Why do you have 4 stages rather than two? You have 4 stages for entree * sauce * sauce * sauce. Why? Why not two stages for Entrees and Sauces. With two stages you would do the exact same thing you did, but without the additional two stage. 5C3 (choose 3 entrees from five entrees) * 2 (sauces).

It would help if you actually defined each stage.
For example:
STAGE 1: Choose 3 entrees
This stage can be completed in 5C3 (aka 10) ways

STAGE 2: What is happening here?
Is it "Choose a sauce"?
If so, which entree are you choosing a sauce for? Each entree must have its own accompanying sauce.
So, for example, ONE outcome (aka meal) might be: chicken with chili sauce, beef with garlic sauce, and vegetable with chili sauce

RefError wrote:
Okay, here you go...
2. Why is it also not appropriate to calculate as Option 1 + Option 2 + Option 3? Option 1 = 5 entrees * 2 sauces. Option 2 = 4 entrees * 2 sauces. Option 3 = 3 entrees * 2 sauces.


This looks like you are repeating many possible meals. So, your answer will be far too big.
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Re: Schezwan restaurant offers 5 chicken, prawn, beef, vegetable & tofu &nbs [#permalink] 24 Sep 2018, 06:49
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