Permutations Practice Test 1

Question : 39 of 40

Marks: +1, -0

In a certain city, all the telephone numbers have six digits, the first two digits always being 41 or 42 or 46 or 62 or 64. The number of telephone numbers having all the six digits distinct is:

9,200
7,200
8,400
1,200

Validate

Solution:

The first two digits can be filled in five ways.
and the remaining 4 digits can be filled in

^8P_4

ways.
Total number of ways =

5 × ^8P_4

= 5 × 1,680 = 8,400

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