Q.

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

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a

6

b

7

c

8

d

9

answer is B.

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Detailed Solution

Distinct n digit numbers which can be formed using digits 2, 5 and 7 are 3n . We have to find n so that3n≥900⇒3n−2≥100⇒n−2≥5 or n≥7So, the least value of n is 7.
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