Dialling a telephone number an old man forgets the last two digits remembering only that these are different dialled at random. The probability that the number is dialled correctly is `1//45` b. `1//90` c. `1//100` d. none of these

Options

A. `1//45`
B. `1//90`
C. `1//100`
D. none of these

Answer

B

Explanation

There are 10 digits 0, 1, 2, 3, 4, 5, 6, 7, 8, 9. The last two digits can be dialled in `.^(10)P_(2)` = 90 ways out of which only one way is favorable, thus, the required probability is `1//90`.