Ratio: Loh Sneakers

 Mr. Loh had some sneakers in his shop. 3/8 of them were red, 3/10 of the remainder were black, and the rest were white.

The table above shows the amount he earned per pair of shoes. The number of red shoes sold to the number of black shoes sold to the number of white shoes sold was 1 : 2 : 4. In total, he sold one quarter of the shoes and earned $1,080. How many pairs of white shoes did have at first ?

Solution:

Draw the model first to describe the shoes available in the store.

Draw the model for pair of shoes sold.

Combine the information of sold pair of shoes with total money he earned:

p(8) + 2p(11) + 4p(15) = 1080 --> 90p = 1080 --> p = 12

So, total sold = 12p = 84 pair of shoes, which is 1/4 of the original number.

It means there are 336 pair of shoes at first, which is

336 = 16u --> u = 21 (refer to first picture)

The number of white pair of shoes = 7u = 147.