2022 AMC 8 Problem 21

Attempt Problem 21 of the 2022 AMC 8 below, then check your answer against the professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2022 AMC 8 solutions, or check the answer key.

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

21.

Steph scored 1515 baskets out of 2020 attempts in the first half of a game, and 1010 baskets out of 1010 attempts in the second half. Candace took 1212 attempts in the first half and 1818 attempts in the second. In each half, Steph scored a higher percentage of baskets than Candace. Surprisingly they ended with the same overall percentage of baskets scored. How many more baskets did Candace score in the second half than in the first?
77
88
99
1010
1111
Answer: C
Concepts:percentageinequality
Small hint:
Steph made 2525 baskets in 3030 attempts overall
Big hint:
Candace must also have made 2525 baskets total
Solution:
Steph made 2525 baskets in 3030 attempts. Candace also took 12+18=3012+18=30 attempts, and their overall percentages were the same, so Candace also made 2525 baskets.
Let ff be Candace’s first-half baskets and ss be her second-half baskets. Then f+s=25f+s=25.
Steph’s first-half percentage was 1520=34\frac{15}{20}=\frac34, so f12<34\frac{f}{12}<\frac34, giving f<9f<9. Steph’s second-half percentage was 11, so s<18s<18.
Thus f≤8f\le8 and s≤17s\le17. Since f+s=25f+s=25, the only possibility is f=8f=8 and s=17s=17, so s−f=9s-f=9.
Thus, the correct answer is C.
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