the simple interest and the true discount on a certain sum for a given time and at a given rate are rs . 85 and rs . 75 respectively . the sum is :
"sol . sum = s . i . * t . d . / ( s . i ) - ( t . d . ) = 85 * 75 / ( 85 - 75 ) = rs . 637.5 . answer b"
divide(multiply(85, 75), subtract(85, 75))