2022 AMC 8 Problem 17
Attempt Problem 17 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).
17.
If is an even positive integer, the double factorial notation represents the product of all the even integers from to For example:
What is the units digit of the following sum?
Answer: B
Small hint:
Any even double factorial at least has a factor of
Big hint:
Only and can affect the units digit
Solution:
For every even the product contains a factor of so that term has units digit Only the first four terms can affect the units digit.
They sum to Therefore the full sum has units digit
Thus, the correct answer is B.
Problem 17 in other years
- 1985 AMC 8
- 1986 AMC 8
- 1987 AMC 8
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- 1989 AMC 8
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- 1991 AMC 8
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