1987 AMC 12 Problem 3
Attempt Problem 3 of the 1987 AMC 12 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 1987 AMC 12 solutions, or check the answer key.
All problems are used with official legal permission of the Mathematical Association of America (MAA).
3.
How many primes less than have as the ones digit? (Assume the usual base representation.)
Answer: C
Small hint:
List every positive integer below whose ones digit is
Big hint:
For numbers below trial division only requires primes through their square roots
Solution:
The primes are The other candidates are composite: and Hence there are such primes.
Thus the correct answer is C.
Problem 3 in other years
- 1950 AMC 12
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