Question

A boardwalk that is x feet wide is built around a rectangular pond. The combined area of the pond and the boardwalk is 4x^2+140x+1200 square feet. What are the dimensions of the pool?
a. 100 ft by 60 ft c. 55 ft by 70 ft
b. 30 ft by 40 ft d. 15 ft by 80 ft
...?

Answer 1

So when X is 0, the area of the pool is 1200. That makes A and C impossible... then you can plug in numbers...say the boardwalk is 1 ft wide, add 2 to each dimension and plug in 1 for X. (You're adding 2 because there is a tile on either side of each dimension, including corners).

32x42=1344=4+140+1200

Therefore the answer is B.