Bob and I got a phone call last night from our favorite nine-year-old, Wen-Ting Wong. She needed help on her math homework. The question was: For every prime number greater than 10, which digits are possible in the one's place?
a. 1, 3, 7, 9
b. 1, 3, 5, 9
c. 0, 2, 4, 5, 6, 8
d. 1, 3, 7
This is 4th grade math. Bob and I resorted to Google. Do you know the answer?