a sum of money at simple interest amounts to rs . 815 in 3 years and to rs . 865 in 4 years . the sum is :
"s . i . for 1 year = rs . ( 865 - 815 ) = rs . 50 . s . i . for 3 years = rs . ( 50 x 3 ) = rs . 150 . principal = rs . ( 815 - 150 ) = rs . 665 . answer : option a"
subtract(815, divide(multiply(subtract(865, 815), 3), 4))