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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
A.
6
B.
7
C.
8
D.
9
E.
None of the above
View Answer
Correct choice: B
Explanation:
Since at any place, any of the digits 2, 5 and 7 can be used, total number of such positive n- digit numbers are 3
n
. Since we have to form 900 distinct numbers, hence 3
n
≥ 9000⇒ n = 7.
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