in a school with 600 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 = ( 600 - x ) . then , ( 11 3 / 4 × 600 ) ⇔ 11 x + 12 ( 600 - x ) ⇔ x = 7200 - 7050 ⇔ 150 . answer a"
subtract(multiply(12, 600), multiply(add(11, divide(9, 12)), 600))