7th Grade Challenging Math

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7-71)   Answers

          (a)   240 mm²

            (b)  80 mm²

            (c)  15a²
 

Solution:
a) Divide ABCD as shown in the figure. Rectangle ABCD contains 15 squares with side length of a. Therefore the ratio of the area in blue and the area of ABCD is 6 to 15. Therefore the area of rectangle EFGH is 600 * 6/15 = 240 mm2.