posted by jenny on .
how many 7 digit telephone numbers can be made if every other digit is even
Not sure if the 7 digit can start with a zero, looked at my phone book and couldn't find any
EOEOEOEOE , assuming the 0 with the evens
number = 4x5x5x5x5x5x5 = 4x5^6 = 62500
or could be
number = 5^7 = 78125
for a total of 140625