what is the average of first 20 multiples of 7 ?
"required average = 7 ( 1 + 2 + . . . . + 20 ) / 20 ( 8 / 20 ) x ( ( 20 x 21 ) / 2 ) ( because sum of first 21 natural numbers ) = 84 d"
multiply(divide(divide(multiply(20, add(20, const_1)), const_2), 20), 7)