1991 AMC 8 Problem 25
Attempt Problem 25 of the 1991 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 1991 AMC 8 solutions, or check the answer key.
All problems are used with official legal permission of the Mathematical Association of America (MAA).
25.
An equilateral triangle is originally painted black. Each time the triangle is changed, the middle fourth of each black triangle turns white. After five changes, what fractional part of the original area of the black triangle remains black?
Answer: C
Small hint:
After one change the middle fourth turns white, so of the black area remains
Big hint:
Each change multiplies the black area by so after five changes multiply by
Solution:
Each change leaves of the current black area black. After five changes the black fraction is
Thus, the correct answer is C .
Problem 25 in other years
- 1985 AMC 8
- 1986 AMC 8
- 1987 AMC 8
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- 1990 AMC 8
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