2021 AMC 10B Spring Problem 3

Attempt Problem 3 of the 2021 AMC 10B Spring below, then check your answer against the video solution and professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2021 AMC 10B Spring solutions, or check the answer key.

All problems are used with official legal permission of the Mathematical Association of America (MAA).

3.

In an after-school program for juniors and seniors, there is a debate team with an equal number of students from each class on the team. Among the 2828 students in the program, 25%25\% of the juniors and 10%10\% of the seniors are on the debate team. How many juniors are in the program?

5 5

6 6

8 8

11 11

20 20

Answer: C
Concepts:percentagesystem of equations
Difficulty rating: 870
Video solution:
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Written solution:

Let the number of juniors be jj and the number of seniors be s.s. Then, j+s=28j+s = 28 and 0.25j=0.1s.0.25j = 0.1s. This means 2.5j=s,2.5j = s, so 3.5j=28.3.5j = 28. This makes j=8.j=8.

Thus, the correct answer is C .

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