First slide

Permutations

Question

The number of 4-digit numbers with distinct digits is

Moderate

A

504
B

4536
C

4634
D

5040

Solution

Number of ways to fill thousand’s place = 9
Number of ways to fill hundred’s place = 9
Number of ways to fill ten’s place = 8
Number of ways to fill unit place = 7
$∴ 9 \times 9 \times 8 \times 7 = 4536$

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