Comparing by Finding Rates

Problem: “Julie drives 210 kilometres in 3 hours, and Marie drives 340 kilometres in 5 hours.  Who is driving faster on average?” 
Discuss how far Julie and Marie travel in 1 hour.

(Answer: 210 ÷ 3 = 70 km/h, 340 ÷ 5 = 68 km/h. So Julie is travelling faster.)

Problem: “A 500 gram packet of Wheatie Flakes costs $1.85, and a 800 gram packet  of Wheatie Flakes costs $2.88. The supermarket shows the costs in cents per 100  grams. What do the labels show? Which packet is better value?”
(Answer: 185 cents ÷ 5 = 37 cents per 100 grams. 288 cents ÷ 8 = 36 cents per 100  grams. So the bigger packet is better value.)

Problem: “Gather data about different sized packets of a product from a supermarket.
Compare their value by finding the cost in cents per 100 grams for each of the sizes.”
Examples: Worksheet (Material Master 8–28).

Understanding Number Properties:

k grams of flour costs $ j. How would you work out the cost of flour per 100 grams? (Answer: $100j/k per 100 grams)