Dialling a telephone number to his daughter an old man forgets the last two digits and dialled at random remembering only that they are different.The probability that the number dialled is correct is

\frac{1}{10}

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\frac{1}{45}

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\frac{1}{90}

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\frac{1}{135}

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Solution

The correct option is D $\frac{1}{90}$
Total permutations $=^{10} C_{2} * 2! = 90$
Correct number $= 1$
$\Rightarrow P = 1 / 90$

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Dialling a telephone number to his daughter an old man forgets the last two digits and dialled at random remembering only that they are different.The probability that the number dialled is correct is

The correct option is D 190Total permutations =10C2∗2!=90Correct number =1⇒P=1/90

The correct option is D $\frac{1}{90}$
Total permutations $=^{10} C_{2} * 2! = 90$
Correct number $= 1$
$\Rightarrow P = 1 / 90$