PSLE
Sam and Luis have the same total number of coins. Sam has a number of twenty-cent coins and 30 ten-cent coins. The total mass of his coins is 1.221 kg. Luis has a number of twenty-cent coins and 70 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 3.3 g heavier than each ten-cent coin. What is the total mass of Luis's coins in kg?

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

Difference in the number of ten-cent coins.
= 70 - 30
= 40

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

Amount that Luis had less than Sam
= 40 x 10
= 400¢
= $4

(b)
Difference in the mass between 40 ten-cent coins and 40 twenty-cent coins
= 40 x 3.3
= 132 g
= 0.132 kg

Total mass of Luis's coins
= 1.221 - 0.132
= 1.089 kg

Answer(s): (a) Sam, $4; (b) 1.089 kg