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# If the probability of snow is the same every day this week, what is th

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Math Expert
Joined: 02 Sep 2009
Posts: 46297
If the probability of snow is the same every day this week, what is th [#permalink]

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28 Feb 2016, 09:44
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If the probability of snow is the same every day this week, what is the probability of snow on Saturday?

(1) The probability of snow on Monday is 1/7.
(2) The probability having of no snow on both Thursday and Friday is 36/49.

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Math Expert
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Re: If the probability of snow is the same every day this week, what is th [#permalink]

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28 Feb 2016, 19:06
Bunuel wrote:
If the probability of snow is the same every day this week, what is the probability of snow on Saturday?

(1) The probability of snow on Monday is 1/7.
(2) The probability having of no snow on both Thursday and Friday is 36/49.

Hi,

info :-

prob is the same each day

lets see the statements:-

(1) The probability of snow on Monday is 1/7.
straight forward. prob is the same every day, so on saturday too prob=1/7
Suff

(2) The probability having of no snow on both Thursday and Friday is 36/49.
let the Prob of snowing be x, so prob of not snowing= 1-x..
so on two days= (1-x)(1-x)=36/49..
(1-x)^2=(6/7)^2..
so 1-x==6/7 or -6/7..
but xcannot be>1,so 1-x=6/7
or x=1/7
Suff

D

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Re: If the probability of snow is the same every day this week, what is th [#permalink]

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05 Aug 2016, 05:24
Bunuel wrote:
If the probability of snow is the same every day this week, what is the probability of snow on Saturday?

(1) The probability of snow on Monday is 1/7.
(2) The probability having of no snow on both Thursday and Friday is 36/49.

From stimulus

P (Snow )= $$\frac{1}{7}$$ (same on Sun, Mon, Tue, Wed, Thur, Fri, Sat)

P (No Snow)= $$\frac{6}{7} ($$same on Sun, Mon, Tue, Wed, Thur, Fri, Sat)

AIM :- FIND P(Snow) on Saturday

(1) The probability of snow on Monday is$$\frac{1}{7}$$

Since P(Snow) on Monday = P (Snow) on Saturday

So P(Snow) on Saturday = $$\frac{1}{7}$$

SUFFICIENT

(2) The probability having of no snow on both Thursday and Friday is $$\frac{36}{49}$$

We know from Stimulus that P (No snow) on Thursday= P (No Snow) on Friday

therefore P (No Snow) Thursday and P(No Snow)Friday $$= \frac{36}{49} = \frac{6}{7}*\frac{6}{7}$$

Therefore P (Snow) on thursday or friday or saturday (since it is same)$$= 1-\frac{6}{7} = \frac{1}{7}$$

SUFFICIENT

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Re: If the probability of snow is the same every day this week, what is th [#permalink]

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03 Nov 2017, 08:31
Top Contributor
Bunuel wrote:
If the probability of snow is the same every day this week, what is the probability of snow on Saturday?

(1) The probability of snow on Monday is 1/7.
(2) The probability having of no snow on both Thursday and Friday is 36/49.

Target question: What is the probability of snow on Saturday?

Given: The probability of snow is the same every day this week

Statement 1: The probability of snow on Monday is 1/7.
If the probability of snow is THE SAME every day this week, then the probability of snow on Saturday is also 1/7
Since we can answer the target question with certainty, statement 1 is SUFFICIENT

Statement 2: The probability having of no snow on both Thursday and Friday is 36/49.
Let p = probability of snow on Saturday.
Since the probability of snow is the same every day this week, we know that p = probability of snow on Thursday and p = probability of snow on Friday.
Also, (1-p) = probability of NO SNOW on Thursday and (1-p) = probability of NO SNOW on Friday.

Statement 2 says: P(no snow on Thursday AND no snow on Friday) = 36/49
Rewrite as: P(no snow on Thursday) x P(no snow on Friday) = 36/49
Rewrite as: (1-p) x (1-p) = 36/49
Simplify: (1-p)² = 36/49
Solve: (1-p) = 6/7
So, p = 1/7
In other words, the probability of snow on Saturday is 1/7
Since we can answer the target question with certainty, statement 2 is SUFFICIENT

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Re: If the probability of snow is the same every day this week, what is th   [#permalink] 03 Nov 2017, 08:31
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# If the probability of snow is the same every day this week, what is th

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