PSLE
Oscar and David have the same total number of coins. Oscar has a number of twenty-cent coins and 41 ten-cent coins. The total mass of his coins is 0.894 kg. David has a number of twenty-cent coins and 61 ten-cent coins.

1. Who has less money in coins? How much less? Give your answers in this format. (Eg Adam, $12)
2. Each twenty-cent coin is 2.2 g heavier than each ten-cent coin. What is the total mass of David's coins in kg?

(a)
Both boys have the same number of coins. Since David has more ten-cent coins than Oscar, it means that David has less twenty-cent coins than Oscar.  So David has less money.

Difference in the number of ten-cent coins.
= 61 - 41
= 20

Difference in the value of 1 ten-cent coin and 1 twenty-cent coin
= 20 - 10
= 10¢

Amount that David had less than Oscar
= 20 x 10
= 200¢
= $2

(b)
Difference in the mass between 20 ten-cent coins and 20 twenty-cent coins
= 20 x 2.2
= 44 g
= 0.044 kg

Total mass of David's coins
= 0.894 - 0.044
= 0.85 kg

Answer(s): (a) Oscar, $2; (b) 0.85 kg