## Saturday, June 13, 2009

Subscribe to:
Post Comments (Atom)

Subscribe to:
Post Comments (Atom)

- Ariel Goldberg
- My name is Ariel Goldberg and I have been a GMAT tutor for eight years. I have taken the GMAT more than twenty times and scored into the 99th percentile; I like to share my GMAT knowledge with everybody. One of the things I like is to write GMAT quant questions that do reflect the changes in the test. The questions sold by some prep services are outdated in that they reflect the GMAT of three or four years ago, before Pearson took over. So that is where I come in, I provide people with good, real-looking GMAT questions.

Easier to solve using combinatorics.

ReplyDelete8c4 = 8.7.6.5/24 = 70

ReplyDelete6C2 = 15

15/70 = 3/14

Why 6C2 and not 4C2?

ReplyDeleteFelix, here is my thinking.

ReplyDeleteSplit 8 students into two groups: (1) 6 students without bart n lisa; (2) bart n lisa

In how many ways can one select 4 students among 8 students in such a way that bart n lisa are included?

Select 2 from (lisa, bart); select two from the remaining 6.

Total = 2C2*6C2 = 1*15 = 15

Selecting 4 out of 8 = 8C4 = 70

The answer would be = 15/70 = 3/14.

But Ariel says it is D. So I am confused as well.

I think it should be B .... 3/14

ReplyDeleteAns.

Probability of 2 fixed people getting selected = (combination of rest of 2 to be selected)/(Combination of all 4 to be selected)

= 6C2 / 8C4 = 3/14

Total number of different ways by which 4 people can be selected from a group of 8 is 8C4 = 70

ReplyDeletenow we know L and B will be there and the task is to find the remaining two from 6

L B _ _

This can be found using 6 C 2= 15

Probability = 15/ 70 = 3/14