a person while dialing a telephone number forgets the last three digits but remember that exactly two of them are similar he dial Numbers find the probability that number is correct..
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We are looking at last three digits: x y z.
Two of them are similar or the same. So the number can be of the form:
x x y, x y x, y x x
Either x or y can be from 0 to 9 but x ≠ y. So x can be one of the 10 digits and y has to be from the other 9 digits.
Hence the possible outcomes/combinations are:
3 * 10 * 9 = 270
The probability that any number dialled is correct is : 1/270
Two of them are similar or the same. So the number can be of the form:
x x y, x y x, y x x
Either x or y can be from 0 to 9 but x ≠ y. So x can be one of the 10 digits and y has to be from the other 9 digits.
Hence the possible outcomes/combinations are:
3 * 10 * 9 = 270
The probability that any number dialled is correct is : 1/270
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