in a school with 620 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
Choose the correct answer:
A) 150	B) 200	C) 155	D) 350	E) none
<gadget id="calculator">12 * 620</gadget>
<output>7_440</output>

<gadget id="calculator">9 / 12</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">11 + (3/4)</gadget>
<output>47/4 = around 11.75</output>

<gadget id="calculator">(47/4) * 620</gadget>
<output>7_285</output>

<gadget id="calculator">7_440 - 7_285</gadget>
<output>155</output>

<result>C</result>
in a school with 620 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
subtract(multiply(12, 620), multiply(add(11, divide(9, 12)), 620))
"sol . let the number of grils be x . then , number of boys = ( 620 - x ) . then , ( 11 3 / 4 × 620 ) ⇔ 11 x + 12 ( 620 - x ) ⇔ x = 7440 - 7285 ⇔ 155 . answer c"