GMAT Question of the Day: Daily via email | Daily via Instagram New to GMAT Club? Watch this Video

 It is currently 26 Jan 2020, 08:32

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# A bag contains 6 balls of one or more colors. A ball is picked and is

Author Message
TAGS:

### Hide Tags

Intern
Joined: 23 Sep 2018
Posts: 5
A bag contains 6 balls of one or more colors. A ball is picked and is  [#permalink]

### Show Tags

03 Nov 2018, 23:20
1
00:00

Difficulty:

75% (hard)

Question Stats:

22% (01:22) correct 78% (01:50) wrong based on 31 sessions

### HideShow timer Statistics

A bag contains 6 balls of one or more colors. A ball is picked and is found to be red. What's the probability that the bag initially had exactly 6 red balls?

A. 2/7
B. 1/5
C. 3/5
D. 4/5
E. 1/7

This question tests the concept of conditional probability and I really found the solution mind-boggling. It would be great if one of the experts could provide a more comprehensive solution to such problems. The source is not official GMAT but it is a great question from one of the CAT forums and I thought it checks all boxes of a supremely tough 700+ question. This is my first question post and although I did go through the rules of posting twice, I apologise in advance for any discrepancy or bug. Kindly help- Bunuel VeritasKarishma
Senior Manager
Joined: 22 Feb 2018
Posts: 408
Re: A bag contains 6 balls of one or more colors. A ball is picked and is  [#permalink]

### Show Tags

03 Nov 2018, 23:38
3
1
OA: A

probability of drawing 1 red ball, when there is 1 red ball out of 6 total balls $$= \frac{1}{6}$$
probability of drawing 1 red ball, when there are 2 red ball out of 6 total balls$$=\frac{2}{6}$$
probability of drawing 1 red ball, when there are 3 red ball out of 6 total balls$$=\frac{3}{6}$$
probability of drawing 1 red ball, when there are 4 red ball out of 6 total balls$$=\frac{4}{6}$$
probability of drawing 1 red ball, when there are 5 red ball out of 6 total balls$$=\frac{5}{6}$$
probability of drawing 1 red ball, when there are 6 red ball out of 6 total balls$$=\frac{6}{6}$$

probability that there are all 6 reds ball,given that we know 1 drawn ball is red ball $$= \frac{\frac{6}{6}}{\frac{1}{6}+\frac{2}{6}+\frac{3}{6}+\frac{4}{6}+\frac{5}{6}+\frac{6}{6}}=\frac{2}{7}$$
Re: A bag contains 6 balls of one or more colors. A ball is picked and is   [#permalink] 03 Nov 2018, 23:38
Display posts from previous: Sort by