2022 AMC 8

Complete problem set with solutions and individual problem pages

Problem 21 Hard

Steph scored 15 baskets out of 20 attempts in the first half of a game, and 10 baskets out of 10 attempts in the second half. Candace took 12 attempts in the first half and 18 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?

  • A.

    7

  • B.

    8

  • C.

    9

  • D.

    10

  • E.

    11

Answer:C

Solution 1 (Inequalities)

Let x be the number of shots that Candace made in the first half, and let y be the number of shots Candace made in the second half. Since Candace and Steph took the same number of attempts, with an equal percentage of baskets scored, we have x+y=10+15=25. In addition, we have the following inequalities:

\frac{x}{12}<\frac{15}{20} \implies x<9,

and

\frac{y}{18}<\frac{10}{10} \implies y<18.

Pairing this up with x+y=25 we see the only possible solution is (x,y)=(8,17), for an answer of 17-8 = \boxed{\textbf{(C) } 9}.

 

Solution 2 (Answer Choices)

Clearly, Steph made 15 + 10 = 25 shots in total. Also, due to parity reasons, the difference between the amount of shots Candace made in the first and second half must be odd. Thus, we can just test 7, 9, and 11, and after doing so we find that the answer is \boxed{\textbf{(C) } 9}.