If a bag contains 12 quarters, 6 dimes, and 18 nickles, what is the part-to-whole ratio of nickles to all coins?
a) 1: 2
b) 1: 3
c) 1: 4
d) 1: 6

There are 18 nickels and 36 total coins
18:36 is your original proportion, but we can simplify.
Divide by 2
9:18
Divide by 9.
1:2 is your final answer.
A.) is correct.