ProbabilityHard

Question

The number ′a′ is randomly selected from the set {0, 1, 2, 3, . . . . . . , 98, 99}. The number ′b′ is selected from the same set. Probability that the number 3a + 7b has a digit equal to 8 at the units place, is

Options

A.1/16
B.2/16
C.4/16
D.3/16

Solution

Unit digit of 3a = 3, 9, 7, 1
Unit digit of 7b = 7, 9, 3, 1
             
         +          +   

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