Marvin counts six $5 bills. write each value that he counts. what pattern do you see in the one digits of the values he counts?

If the number of bills counted is odd, the ones digit is 5; if the number of bills is even, the ones digit is 0.

Explanation

1) Simulate the counting of the bills:

number of bills counted          value              ones digit

1                                             5                         5

2                                             5 + 5 = 10           0

3                                             10 + 5 = 15         5

4                                             15 + 5 = 20         0

5                                              20 + 5 = 25        5

6                                              25 + 5 = 30        0

2) Pattern: you can see that the ones digit alreternate: 5, 0, 5, 0, 5, 0, ...

If the number of bills counted is odd the ones digit is 5, if the number of bills is even the ones digit is 0.