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Let A be the set of 4-digit numbers a(1)...

Let A be the set of 4-digit numbers `a_(1)a_(2)a_(3)a_(4)` where `a_(1)gta_(2)gta_(3)gta_(4)` then n(A) is equal to

A

126

B

84

C

210

D

315

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The correct Answer is:
C
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