Question

The local seven-digit telephone numbers in city A have 1,8,0, as the first three digits. How many different telephone numbers are possible in city A?

Answer 1

10,000

Step-by-step explanation

Given:

The first-three digits to be 1, 8, 0 out of seven-digit telephone numbers.

Desired outcome:

Total number of possible different telephone numbers

Determine the possibilities of the 4th, 5th, 6th and the 7th digits

The 4th digit has 10 possibilities (i.e: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9)

The 5th also has 10 possibilities,

likewise the 6th and the 7th digits.

Now, we have:

10 x 10 x 10 x 10 = 10^4 = 10,000

Hence, the number of possible different telephone numbers is 10,000.