The cross-section of a trough of height 36 cm is an isosceles trapezium ABCD where AB = 50 cm as shown. If the area of ABCD is 2250 cm2, then find the length of CD in cm.
75
Let the length of CD be x cm.
Area of ABCD = 12 x (AB +CD) x height
[Area of trapezium is half the product of the parallel sides and the distance between them.]
12 x (50 + x) x 36 = 2250
(50 + x) x 18 = 2250
50 + x = 225018
50 + x = 225018
50 + x = 125
x = 125 - 50
x = 75
The length of CD is 75 cm.