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 `3^a + 7^b` has a digit equal to 8 at the units place, is

Two numbers are selected at random from the set {1,2,3,....,13} . If the sum of the selected numbers is even, the probability that both the numbers are odd is

A number is selected from the set {2,3,…,30}. The probability that the selected number is a prime number is

A number is selected from the set {1, 2, 3,.., 20} . The probability That the selected number is divisible by 3 or 4 is

A number is selected from the set {1,2,3, . . .20}. The probability that the selected number is divisible by 3 or 4 is . . .

A coin is tossed. If a head is observed, a number is randomly selected from the set {1, 2, 3} and if a tail is observed, a number is randomly selected from the set {2, 3, 4, 5} . If the selected number be denoted by X, what is the probability that X = 3 ?

From the set of numbers {1,2,3,...,10} , 4 numbers are selected at random. The probability that all of the selected numbers are consecutive is

Three numbers are selected from the set {1,2,3,...,23,24}, without replacement.The probability that the selected numbers form an A.P.is equal to