Permutation and CombinationMedium
Question
An n digit number is a positive number with exactly n digits. Nine hundred n- digit numbers are to be formed using only the three digits 2, 5 and 7. The smallest value of n for ehich this is possible, is
Options
A.6
B.7
C.8
D.9
Solution
Distinct n digit numbers which can be formed using digits 2, 5 and 7 are 3n We have to find n so that
3 n ≥ 900 ⇒ 3n-2 ≥ 100
⇒ n - 2 ≥ 5
⇒ n ≥ 7 so the least value of n is 7.
3 n ≥ 900 ⇒ 3n-2 ≥ 100
⇒ n - 2 ≥ 5
⇒ n ≥ 7 so the least value of n is 7.
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