Question

How many 7-digit numbers are there having the digit 3(three times ) and the digit 0(four times ) ?

• A. 15
• B. $3^3\times 4^4$
• C. 30
• D. None of these

Answer 1

The correct option is A 15


$d_1$
is 3 because we have to form 7 digit number now we have rest six boxes
$d_2,d_3,d_4,d_5,d_6,d_7$
to be filled, this can be done in

$\frac{6!}{2!\times 4!}=15ways$