Question

A telephone number is selected at random from a directory. suppose x denote the last digit of selected telephone number.

A) find the probability that the last digit of the selected number is 6.

B) find the probability that the last digit of the selected number is less than 3.

C) determine the mean and standard deviation of the last digit

Answer 1

a) find the probability that the last digit of the selected number is 6.

there are 10 possibility for last digit

hence probability = 1/10

B) find the probability that the last digit of the selected number is less than 3.

number which are less than 3 are 0,1, and 2

hence required probability = 3/10

C) determine the mean and standard deviation of the last digit

last digit can be 0,1,2,...9

hence mean = sum of all numbers / count of numbers

= 9/2

sd = ((b - a + 1)^2 - 1 )/12   , here a = 0 , b = 9

sd = (10^2 - 1)/12

= 99/12

= 33/4