
Trapezoid problem
Lot 21 is a trapezoid with the two bases perpendicular to the road. The scale drawing below uses 1/2 inch = 40 ft.
http://i996.photobucket.com/albums/a...2/DSC_0451.jpg
A) 1/2 acre
B) 2 acres
C) 2 1/2 acres
D) 3 acres
So here's how I try to solve it:
A = 1/2 x 4 (5 + 3 1/2)
A = 1/2 x 20 x 8 1/2
A= 85
What am I doing wrong? What steps do I take?

Did you use your scale that 1/4 inch equals 40 feet?.
b1: How many 1/2 inches are in 3.5 inches?. 7
7*40=280
b2: How many half inches are in 5 inches?. 10
10*40=400
Proceed in that fashion and you should be OK. It's like that other problem I stepped through involving scales.
Find the square feet form this and then divide by 43,560 to find the acres.

In reallife, scales on blueprints are usually given as 1" = however many feet.
If 1/2 inch is 40 feet, then 1 inch is 80 feet. So, 5 inches would be 400 feet.
You could proceed this way.