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[JEE Advanced 1998] Using only digits $2,5,7$, nine hundred distinct $n$-digit numbers are to be formed. The smallest $n$ is

VAVidaara Admin Asked 1mo ago 1 views 1 answer
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Using only digits $2,5,7$, nine hundred distinct $n$-digit numbers are to be formed. The smallest $n$ is

(a) $6$
(b) $7$
(c) $8$
(d) $9$

1 Answer

VAVidaara Admin ✓ Vidaara Team ✓ Accepted · 1mo ago ▲ 0

Correct answer: (b) $7$

$3^n\ge900$: $3^6=729<900\le3^7=2187$, so $n=7$.

JEE Advanced 1998 · Permutations and Combinations — verified solution by the Vidaara Team.

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