Question

The average of marks scored by the students of a class is 68.The average of marks of the girls in the class is 80 and that of boys is 60.What is the percentage of boys in the class?

Answer 1

$x + 80 \div 2 = 68$
$x + 80 = 68 \times 2$
$x + 80 = 136$
$x = 136 - 80$
$x = 56$