Solve multiplication and division problems that involve decimals.

Number Framework Stage 8

Calculators

#### Using Number Properties

Problem: “Snapper costs $13.89 per kilogram. Maru bought some snapper, and it cost him $56.80.When he got home, he wondered what weight of snapper he had bought.”

Discuss the problem and write it on the board as 13.89 x ? = 56.80.Discuss how to solve such problems and how to round the calculator answer sensibly.

*(Answer: 13.89 *x ? *= 56.80 is the same as ?* *= 56.80 *÷ *13.89 = 4.089272858. As this **is kilograms, it makes no sense to have an answer more accurate than the nearest **gram, that is to say, the nearest 0.001 kilogram. So rounding to 3 decimal places **gives 4.089 kilograms.)*

Problem: “Filbert had 7.475 kilograms of olives. He put a set weight of olives in a setof jars and found he had enough for 13 jars. Write this down as a division problem.”*(Answer: 7.475 *÷ ? *= 13.)*

“Later Filbert wanted to add labels showing the weight of olives in each jar, but he had forgotten what this weight was. How would Filbert solve 7.475 ÷ ? = 13?” *(Answer: 7.475 *÷ ? *= 13 is the same as ?* *= 7.475 *÷ *13 = 0.575 grams.)*

Examples: Worksheet (Material Master 8–2).

##### Understanding Number Properties:

Choose one answer:

If a □ = b □ equals a ÷ b b ÷ a a x b (Answer: b ÷ a)

If a ÷ □ = b □ equals a ÷ b b ÷ a a x b (Answer: a ÷ b)

If □ ÷ a = b □ equals a ÷ b b ÷ a a x b (Answer: a x b)

If □ a = b □ equals a ÷ b b ÷ a a x b (Answer: b ÷ a)