how many phone numbers are possible in the (404) area code if the seven digit number have the form FGH- where F is restricted to 3-9 and X, G and H can be any digit 0-9?

900 phone numbers possible.

Step-by-step explanation:

Given the seven digit numbers are of the form:

FGH-XXXX

Possibilities for F = 3 - 9 and X i.e. 9 possibilities

Possibilities for G = 0 - 9 i.e. 10 digits

Possibilities for H = 0 - 9 i.e. 10 digits

To find:

How many numbers are possible ?

Solution:

This problem is nothing but a problem in which we have to find out how many numbers are possible where each digit has a few options available.

Number of ways to select F = 8 digits from 3 to 9 and 1 alphabet X = 9

Number of ways to select G = 10 digits from 0 to 9

Number of ways to select H = 10 digits from 0 to 9

XXXX part will be same in all the numbers.

So, total phone numbers possible =

Hence, the answer is:

900 phone numbers possible.

or

step-by-step explanation:

we need to solve for 'x' the following equation:  

we have that:

⇒

⇒ ⇒

factorizing, we get that:

  ⇒

then, the solutions are: or

nothing extraneous has been found!