Question

Social Security numbers are of the formXYZ - MN - ABCD.The first three digits XYZ are referred toas the area number. The number isassociated with where you registered foryour social security card. X is a number 1- 7. Y and Z can be any number 0 - 9.Also the area number 666 has neverbeen used. How many area numbers arepossible?

Answer 1

How many area numbers are possible?

Area numbers are XYZ,

where X goes from 1 to 7, and Yand Z go from 0 to 9

additionally, 666 has never been used

$\frac{7}{X}\cdot\frac{10}{Y}\cdot\frac{10}{Z}=700$

There are 700 possible combinations, but if we exclude 666, now we have 699 possible combinations