The letters A, B, C, D, E and F are randomly placed in a row. The probability that the letters A and B will occupy the first and second positions respectively is:

A 1/15

B 1/3

C 1/30

D 1/6

E 2/3

Question

The letters A, B, C, D, E and F are randomly placed in a row. The probability that the letters A and B will occupy the first and second positions respectively is:

A  1/15

B  1/3

C 1/30

D 1/6

E  2/3

ganpat · Answer

letter A occupying 1st seat = 1 out of 6 = 1/6
than letter B occupying second seat = 1 out of 5 = 1/5

so, 1/6 * 1/5 = 1/30..

option C ??

anonymous · Answer

yes it is.

anonymous · Answer

how can you differentiate between using permutations nPr or combinatorics nCr?

ganpat · Answer

Combination is way for selecting things from a group.. 
for example: selecting a red ball from a group of 15 balls of different colors..
 
While, Permutation you can say, arrangement of things as per demand.. 
for example: arrange 10 books, such that 4 & 5 stay together..

This is what i can explain in simplest... Hope u understand..

ganpat · Answer

http://www.mathsisfun.com/combinatorics/combinations-permutations.html refer this, for understanding...

anonymous · Answer

okok, thanks.

ganpat · Answer

anytime :)