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Question: Dialing a telephone number an old man forgets the last two digits remembering only that these are di...

Dialing 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

A

145\frac { 1 } { 45 }

B

190\frac { 1 } { 90 }

C

1100\frac { 1 } { 100 }

D

None of these

Answer

190\frac { 1 } { 90 }

Explanation

Solution

There are 10 digits 0,1,2,3,4,5,6,7,8,90,1,2,3,4,5,6,7,8,9 The last two digits can be dialled in 10P2=90{ } ^ { 10 } P _ { 2 } = 90 ways, out of which only one way is favourable, thus the required

probability =190= \frac { 1 } { 90 }