Free sample · Primary 5

Decimal cost from a rate

multiplying a unit price by a decimal mass to find total cost.

I Do

Worked example

Apples cost S＄3.00 per kilogram. Mei buys 2.4 kg. What is the total cost?

Picture the bag on a scale: 2.4 kg at S$3.00 for each kilogram.

Total cost = rate × mass = $3.00 \times 2.4$ .

$3 \times 2 = 6$ , and $3 \times 0.4 = 1.2$ , so $3.00 \times 2.4 = 7.2$ . The cost is S＄7.20.

Move: multiply the unit price by the mass. Why: each kilogram costs S＄3.00, so 2.4 kilograms cost 2.4 times that amount.

We Do

Try this step

Oranges cost S＄2.50 per kilogram. Kai buys 1.6 kg. What is the total cost?

You Do

On your own

Flour costs S＄1.80 per kilogram. Rina buys 3.5 kg. What is the total cost?

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