In the country Fivethree, they have only $3 and $5 notes. How many amounts, from $1 to $100 inclusive, cannot be made up exactly with these notes?
A. 2
B. 3
C. 4
D. 7
E. 21
1,2,4,7 cannot be made
I think you can easily show that all the rest are multiples of 3 or 5, or can be made using them and makeable remainders.