Question
Question: If the integer a and b are chosen at random between 1 and 100, then the probability that 7<sup>a</su...
If the integer a and b are chosen at random between 1 and 100, then the probability that 7a + 7b is divisible by 5, is
A
41
B
81
C
71
D
491
Answer
81
Explanation
Solution
7a always ends with 7, 9, 3, 1.
\7a + 7b is divisible by 5
̃ Favourable events = (25 × 25) × 2
And sample space = 100 × 100
Required probability = 100×1002(25×25)= 81