Seven-digit telephone numbers are not allowed to begin with 0 or 1. I can only remember a seven-digit telephone number if the first three digits (the "prefix") are equal to the next three digits or the last three digits. For example, I can remember 389 - 3892 and 274 - 9274. How many seven-digit telephone numbers can I remember?
+118609 Seven-digit telephone numbers are not allowed to begin with 0 or 1. I can only remember a seven-digit telephone number if the first three digits (the "prefix") are equal to the next three digits or the last three digits. For example, I can remember 389 - 3892 and 274 - 9274. How many seven-digit telephone numbers can I remember?
abcabc* or abc*abc
a cannot be 0 or 1 so 8 choices
2* 8*10*10* 10 = 16000
