1999 AMC 8 Problem 5

Attempt Problem 5 of the 1999 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 1999 AMC 8 solutions, or check the answer key.

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

5.

A rectangular garden 5050 feet long and 1010 feet wide is enclosed by a fence. To make the garden larger, while using the same fence, its shape is changed to a square. By how many square feet does this enlarge the garden?
100100
200200
300300
400400
500500
Answer: D
Concepts:perimeterarea
Small hint:
Keep the perimeter the same
Big hint:
The square side length is one-fourth of the old perimeter
Solution:
The current length of the fence is 2(50+10)=2⋅60=120 2(50 + 10) = 2 \cdot 60 = 120 feet. If all the sides become the same, then each side length is 120÷4=30 120 \div 4 = 30 feet. As such, the area of the square is then 302=900 30^2 = 900 square feet. Note that the original area of the garden is 50⋅10=500 50 \cdot 10 = 500 square feet.
Therefore, the difference is 900−500=400 900 - 500 = 400 square feet.
Thus, D is the correct answer.
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