Question

A telephone number consists of seven digits, the first three representing the exchange. how many different telephone numbers are possible within the 537 exchange g

Answer 1

we have that

1) Subtract 3 from 7, because the exchange is always the same.
that leaves 4 numbers
the number of possible digits in each number is 10
therefore
possibilities=10*10*10*10=10000 numbers

the answer is 10000