Question

Out of 20 consecutive whole numbers two are chosen at random. Then the probability that their sum is odd is ______ 

(a) (5/19)

(b) (10/19)

(c) (9/19)

(d) (11/19).

Answer 1

The correct option  (b) (10/19)  

Explanation:

Of 20 consecutive whole numbers, 10 are even and 10 are odd. Sum is odd if one is even and other is odd.

∴ Required probability  = [{(¹⁰C₁)(¹⁰C₁)}/(²⁰C₂)]

= [(10 × 10)/190]

= (10/19).