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Question

An n-digit number is a positive number with exactly n digits. Nine hundred distinct n-digit numbers are to be formed using only the three digits 2, 5 and 7. The smallest value of n for which this is possible is


A

6

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B

7

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C

8

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D

9

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Solution

The correct option is B

7


Since at any place, any of the digits 2, 5 and 7 can be used, total number of such positive n-digit numbers are 3n. Since we have to form 900 distinct numbers, hence 3n900n = 7


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