Telephone numbers are preceded by a 3-digit area code (e.g. 437). In the following questions, any digit from {0, 1, 2, 3, 4, 5,

Question

Telephone numbers are preceded by a 3-digit area code (e.g. 437). In the following
questions, any digit from {0, 1, 2, 3, 4, 5, 6, 7, 8, 9) can be used unless otherwise stated.
How many area codes are possible if:
a. the first digit must be 1?
b. the third digit must not be 4?
c. the second and third digits must be the same?
d. neither 1 nor 2 must be used?

Kunduz · Accepted Answer

Click to see the answer