the cross - section of a river bank is a trapezium in shape . if the river bank is 12 m wide at the top and 8 m wide at the bottom and the area of cross - section is 500 sq m , the depth of river bank is ?
1 / 2 * d ( 12 + 8 ) = 500 d = 50 answer : d
divide(500, divide(add(12, 8), const_2))