Question

every student in a homeroom class takes a biology course or a spanish course or both. if 18 take biology, 13 take spanish and 5 take both, how many students are in the homeroom classroom?

Answer 1

Answer: 26

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Work Shown:

A = 18 take bio

B = 13 take Spanish

C = 5 take both

A+B-C = 18+13 - 5 = 26 students total

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Another approach:

18 take bio and 5 take both, so 18-5 = 13 take bio only

13 take Spanish and 5 take both, so 13-5 = 8 take Spanish only

We then have 13+8+5 = 26 students

Both methods only work when each student is in either bio, Spanish, or both. We cannot have a student who is in neither class.