Please help me. I cannot find online the solution to this question. It is a prob

Question

Please help me. I cannot find online the solution to this question.

It is a probabilty question.

A person has forgotten the last digit of a telephone number, so he dials the number with the last digit randomly chosen.

How many times does he have to dial (if he does not dial the same number twice) in order that the probability of dialing the correct number is more than 0.65.

How many times does he have to dial (if he may dial the same number twice) in order that the probability of dialing the correct number is more than 0.65.

Explanation / Answer

The probabilty of dailing correct number = correct number/no. of chance =1/10

By not counting repititions we are dailing the number within probability of daling correct number is more than 0.65 is

(n)*(1/10)> 0.65

where n is number of dails

n> 0.65*10
n>6.5

the minimum possible n=7

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