1. Marlin averages for his Social Studies class is listed below. If the teacher weights homework at 20%, quizzes at 20%, tests at 45%, and the final exam
at 15%, what is Marlin's class average?
1)61%
2)71%
3)74%
4)82%

we have three similar triangles, because each has a right angle and shares an angle.   let's write the angles in order: opposite to short leg, long leg, hypotenuse.

cab similar to bad similar to cbd

or as ratios,

ca: ab: cb = ba: ad: bd = cb: bd: cd

we also know

ac = ad + cd

(ad+cd): ab: cb = ba: ad: bd = cb: bd: cd

(ad+cd)/cb=cb/cd

we have cb=6, ad=5 and seek x=cd.

we reject the negative root and conclude x=4

answer: 4

the answer is b