in a school with 652 students , the average age of the boys is 12 years and that of the girls is 11 years . if the average age of the school is 11 years 9 months , then the number of girls in the school is
"sol . let the number of grils be x . then , number of boys = ( 652 - x ) . then , ( 11 3 / 4 × 652 ) ⇔ 11 x + 12 ( 652 - x ) ⇔ x = 7824 - 7661 ⇔ 163 . answer d"
subtract(multiply(12, 652), multiply(add(11, divide(9, 12)), 652))