AP EAMCET Engineering 21 Apr 2019 Shift 1 Paper

The is given that A and B each select one number at random from the distinct number 1,2,3,...,n then the probability that the number selected by A is less than selected by B, ‌

nC2

n×n

‌‌=‌

n(n−1)

2(n×n)

‌‌=‌

1009

2019

Thus,
‌

n−1

2n

‌‌=‌

1009

2019

n‌‌=2019

Now number of ways selecting a number from 1,2,3,...,2019 by B is the number immediately next to the number selected by A is 2018. So the required probability is,

‌

2018

2019×2019

=‌

2018

(2019)2