How many girls are in the school if 40% of a school population is made up of 240 boys?
100% - 40% = 60% of the school's population are girls.
Since 40% is equal to 240 students, then 1% is equal to 240/40 = 
<gadget id="calculator">240/40</gadget>
<output>6</output>
6 students.
Hence, there are 60 x 6 = 
<gadget id="calculator">60*6</gadget>
<output>360</output>
360 girls.

<result>360</result>