Find the area of this isosceles trapezoid. A) 85.5 units2 B) 171 units2 C) 342 units? 345 units?​

9514 1404 393

  B) 171 units^2

Step-by-step explanation:

The area is given by the formula ...

  A = 1/2(b1 +b2)h

Filling in the given base and height values, we find the area to be ...

  A = 1/2(23 +15)(9) = (19)(9) = 171 . . . square units

Additional comment

You can select the correct answer choice simply on the basis of "reasonableness." If this were a 9×15 rectangle, its area would be 9×15 = 135 square units, more than 85.5. You know its area is less than a 9×23 rectangle, so is less than 9×23 = 207 square units. Only one answer choice is a value between 135 and 207.

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Multiplication by 9 is not so hard. It is multiplication by 10-1:

  15×9 = 15×(10 -1) = 150 -15 = 135