A Bag Contains 2 White and 3 Red Balls, And a Bag B Contains 4 White GMAT Problem Solving

Question: A bag contains 2 white and 3 red balls, and a bag B contains 4 white and 5 red balls. One ball is drawn at random from one of the bags and it is found to be red.

Find the probability that it was drawn from the bag B

  1. 5/52
  2. 15/52
  3. 25/52
  4. 35/52
  5. 45/52


Correct Answer:
C

Solution and Explanation
Approach Solution 1:
There is only one way to solve this problem. The approach is to solve it by using the method of probability.

This is a conditional probability problem since it is asking: given that the ball is red, what is the probability it is from bag B?
We can use the following formula:
P(bag B, given it’s a red ball) = P(a red ball from bag B)/P(a red ball)
Let us assume that there is an equal chance of picking either bag, we have:
P(a red ball from bag B)
= 5/9 x 1/2
= 5/18
P(a red ball) = P(a red ball from bag B) + P(a red ball from bag A)
= 5/9 x 1/2 + 3/5 x 1/2
= 5/18 + 3/10
Therefore, as per the equation the probability in question is:
(5/18)/(5/18 + 3/10)
Now, we will Multiply the numerator and the denominator by 90, we have:
25/(25 + 27) = 25/52
 

“A bag contains 2 white and 3 red balls, and a bag B contains 4 white”- is a topic of the GMAT Quantitative reasoning section of GMAT. To solve GMAT Problem Solving questions a student must have knowledge about a good amount of qualitative skills. GMAT Quant practice papers improve the mathematical knowledge of the candidates as it represents multiple sorts of quantitative problems.


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