Question
How many five digit telephone numbers can be constructed using the digits 0 to 9. If each number starts with 67 and no digit appears more than once?

Answer

Total number of digits = 10
each number starts with 67 and no digit appears more than once.
$\therefore$ Total number of five digit telephone numbers.
= 1 × 1 × 8 × 7 × 6 = 336

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