1989 AIME Problem 1

Attempt Problem 1 of the 1989 AIME 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 1989 AIME solutions, or check the answer key.

All problems are used with official legal permission of the Mathematical Association of America (MAA).

1.

Compute (31)(30)(29)(28)+1.\sqrt{(31)(30)(29)(28)+1}.
Answer: 869
Concepts:difference of squaresfactoringradical
Small hint:
Pair the outer factors and the inner factors
Big hint:
The two paired products are consecutive even integers
Solution:
We have 31⋅28=86831\cdot28=868 and 30⋅29=870.30\cdot29=870. These products lie one below and one above 869,869, so their product is 8692−1.869^2-1. After the final 11 is added, the radicand is 8692.869^2. Its positive square root is 869.869.
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