Final answer:
By setting up and solving a system of equations based on the information given, we find that Leo had 170 Singapore stamps left after giving some away, corresponding to option b.
Step-by-step explanation:
The problem presented is a mathematical word problem involving proportions and percentages. Initially, we are told that the number of Singapore stamps that Leo had was 4/3 the number of foreign stamps. Let the number of foreign stamps be F, then the number of Singapore stamps is 4/3 F. After giving away 68 Singapore stamps and 12 foreign stamps, we are informed that the number of Singapore stamps became 20% of the total number of stamps he had left.
Let's denote the remaining number of Singapore stamps as S and the remaining number of foreign stamps as F. After giving away some stamps, the relations will be: S = 4/3 F - 68 and F = F - 12. Now, S is also 20% (or 1/5) of the total stamps left, meaning S = 1/5(S + F).
Solving this system of equations:
S = 4/3 (F - 12) - 68
S = 1/5(S + F - 12)
We can derive the numbers of stamps. Eventually, we find that S, the number of Singapore stamps Leo had after giving some away, is 170, which corresponds to option b.