You have 90 minutes to complete at least 18 chemistry and math problems. It takes 5 minutes to complete a chemistry problem and 4 minutes for each math problem. how many chemistry problems are there

Answer 1

As written, there are multiple possible solutions:

C+M >= 18 and 5C+4M <= 90

If C = 0, 4M <= 90 so 18 <= M <= 22

If C = 1, 4M <= 85 so 17 <= M <= 21

...

If C = 18, M = 0

Thus 0 <= C <= 18