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.