1987 AIME Problem 1

Attempt Problem 1 of the 1987 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 1987 AIME solutions, or check the answer key.

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

1.

An ordered pair (m,n)(m,n) of nonnegative integers is called “simple” if adding m+nm+n in base 1010 requires no carrying. Find the number of simple ordered pairs that sum to 1492.1492.
Answer: 300
Concepts:digitsplace valuemultiplication principle
Small hint:
Treat the four decimal places independently
Big hint:
A target digit dd can be split into an ordered pair of digits in d+1d+1 ways without carrying
Solution:
For a target digit d,d, there are d+1d+1 ordered pairs of nonnegative digits with sum d.d. The four digits 1,1, 4,4, 9,9, 22 therefore give 2,2, 5,5, 10,10, 33 choices independently. The answer is 2⋅5⋅10⋅3=300.2\cdot5\cdot10\cdot3=300.
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