Jon P. answered 04/29/15
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Harvard honors degree in math, experienced geometry tutor
Try to write out exactly what it says, in "algebra":
"find the measure of angle" -- They want you to find the angle, so call the angle x
"whose supplement" -- that's 180 - x
"is" -- that means, equals or =
"10 times" -- 10 *
"its complement" -- that's 90 - x
So that gives you an equation:
180 - x = 10 * (90 - x)
Just solve it...
180 - x = 10 * (90 - x)
180 - x = 900 - 10x
180 - x + 10x - 900
180 + 9x = 900
9x = 720
x = 80
So the angle is 80°. Check the answer by seeing if the statement about the angle is correct.