Q.

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

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a

6

b

7

c

8

d

9

answer is B.

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Detailed Solution

The number of n-digit distinct numbers that can be formed using digits 2, 5 and 7 is 3n. We have to find n, so that 3n≥900⇒ 3n−2≥100 ⇒ n−2≥5 ⇒ n≥7Thus, the smallest value of n is 7
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