SOLUTION: On a trapezoid if the top is 3x-1, the middle is labeled with 40, and the bottom is 8x+4 what is the formula to solve for x? Thank you!

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Question 129522: On a trapezoid if the top is 3x-1, the middle is labeled with 40, and the bottom is 8x+4 what is the formula to solve for x?
Thank you!
Answer by scott8148(6628) About Me  (Show Source):
You can put this solution on YOUR website!
the middle is the arithmetic mean between the top and the bottom

((3x-1)+(8x+4))/2=40 __ 11x+3=80 __ 11x=77