Question

a box half full of apples weighs 40kg and the same box one fifth full weighs 22kg, what does the box weigh when empty?

Answer 1

1/2 = 40kg
1/5 = 22kg
1/2 = 5/10
1/5 = 2/10
3/10 is the difference between 18kg.
This means 1/10 of the box filled with apples is 6kg.
40 - (5 x 6) = 10kg. The box weighs 10kg alone. 

Answer 2

1/2 = 40kg
1/5 = 22kg
1/2 = 5/10
1/5 = 2/10
3/10 is the difference between 18kg.
This means 1/10 of the box filled with apples is 6kg.
40 - (5 x 6) = 10kg. The box weighs 10kg alone.