Today’s ACT question is about the area of a trapezoid – they were nice enough to give us that formula right in the problem, so it’s a piece of cake! Careful substitution cake with algebra frosting.
The formula they give us is:
a = (1/2)*h*(b1 + b2) (h is the altitude, b1 and b2 are the parallel bases)
Then they tell us that h = 5, a = 55, and one base = 13. We are asked to find the other base. Time to plug in some numbers!
55 = (1/2) * 5 * (13 + x)
22 = 13 + x
9 = x
Check:
.5 * 5 * (13 + 9) = 55
F, 9, is the answer.
If you substitute carefully and avoid arithmetic errors, problems like this one will breeze by!