2015 AMC 8 Problem 9
Attempt Problem 9 of the 2015 AMC 8 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 2015 AMC 8 solutions, or check the answer key.
All problems are used with official legal permission of the Mathematical Association of America (MAA).
9.
On her first day of work, Janabel sold one widget. On day two, she sold three widgets. On day three, she sold five widgets, and on each succeeding day, she sold two more widgets than she had sold on the previous day. How many widgets in total had Janabel sold after working days?
Answer: D
Small hint:
The daily sales are the first positive odd numbers.
Big hint:
Pair the first and last terms, second and next-to-last terms, and so on.
Video solution:
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Written solution:
We want to find Pairing terms from the ends gives There are pairs, and each pair sums to Therefore, the sum is
Thus, the correct answer is D .
Problem 9 in other years
- 1985 AMC 8
- 1986 AMC 8
- 1987 AMC 8
- 1988 AMC 8
- 1989 AMC 8
- 1990 AMC 8
- 1991 AMC 8
- 1992 AMC 8
- 1993 AMC 8
- 1994 AMC 8
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- 1998 AMC 8
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