Asked by jenny

how many 7 digit telephone numbers can be made if every other digit is even
Answered by Reiny
Not sure if the 7 digit can start with a zero, looked at my phone book and couldn't find any

could be
EOEOEOEOE , assuming the 0 with the evens
number = 4x5x5x5x5x5x5 = 4x5^6 = 62500

or could be
OEOEOEO
number = 5^7 = 78125

for a total of 140625