### Solution 3 & 4

Solution 3

In a camp , 48 campers are boys .
The ratio of the number of boys to the number of girls is 3 : 1 .
The fraction of the number of non-swimmers over swimmers in the camp is 1/7 .
If 25% of the non-swimmers are girls, how many boys can swim ?

(Draw a model*)

6 units = 48
1 unit = 8      (Non-swimmers)
75% x 8 = 6  (Non-swimmer boys)
48 - 6 = 42

There are 42 boys who can swim .

Solution 4

Tap A takes 8 minutes to fill an empty fish tank of dimension 40 cm width by 120 cm length and unknown height with water to the brim.
Tap B takes 6 minutes to fill the same empty fish tank with water to the brim.
Tap C takes 4 minutes to drain all the water out from the full fish tank.
How long does it take for the water to overflow from the fish tank, given that the fish tank is half-filled and all 3 taps are turned on at the same time?

Lowest common multiple of 4 , 6 and 8 = 24

Given time = 24 minutes :
Tap A would fill 3 fish tanks
Tap B would fill 4 fish tanks
Tap C would drain 6 fish tanks

In 24 minutes , Tap A + Tap B + Tap C = 3 + 4 - 6 = 1 fish tank filled

Therefore with all 3 taps turned on , 1 fish tank will be filled with water in 24 minutes

Given that fish tank is half-filled and to fill the other half :
Time taken = 24 / 2 = 12 minutes

It takes 12 minutes for water to overflow from the fish tank .