How to find the length of the side of a trapezoid

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ISEE Upper Level Quantitative Reasoning › How to find the length of the side of a trapezoid

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Trapezoid

Note: Figure NOT drawn to scale.

The area of the above trapezoid is . What is ?

Substitute into the formula for the area of a trapezoid:

$\frac{1}{2} (B + b)h = A$

$\frac{1}{2} (B + 25) \cdot 15 = 465$

$2 \cdot \frac{1}{2} (B + 25) \cdot 15 = 2 \cdot 465$

$(B + 25) \cdot 15 = 930$

$15 B \div 15 = 555\div 15$