PSLE
Billy and Justin have the same total number of coins. Billy has a number of fifty-cent coins and 45 twenty-cent coins. The total mass of his coins is 0.947 kg. Justin has a number of fifty-cent coins and 75 twenty-cent coins.

1. Who has more money in coins? How much more? Give your answers in this format. (Eg Adam, $12)
2. Each fifty-cent coin is 3.4 g heavier than each twenty-cent coin. What is the total mass of Justin's coins in kg?

(a)
Since Billy has less twenty-cent coins than Justin but both had the same number of coins, Billy had more money.

Both boys have the same number of coins. Since Billy has less twenty-cent coins than Justin, it means that Billy has more fifty-cent coins than Justin. So Billy has more money.

Difference in the number of twenty-cent coins.
= 75 - 45
= 30

Difference in the value of 1 twenty-cent coin and 1 fifty-cent coin
= 50 - 20
= 30¢

Amount that Billy had more than Justin
= 30 x 30
= 900¢
= $9

(b)
Difference in the mass between 30 twenty-cent coins and 30 fifty-cent coins
= 30 x 3.4
= 102 g
= 0.102 kg

Total mass of Justin's coins
= 0.947 - 0.102
= 0.845 kg

Answer(s): (a) Billy, $9; (b) 0.845 kg