The best value isn't always the cheapest pack — a bigger pack costs more but might be cheaper for the same amount. To compare fairly, work out the unit price: how much it costs per 100 g. Divide the price (in cents) by how many 100 g lots the pack holds. A 500 g pack for 400 c is 400 ÷ 5 = 80 c per 100 g. Whichever pack has the lower cents per 100 g is the better value.
Explore this idea with maths tools
Maths you can move
Build 8 + 5
Tap two gold counters to fill the ten-frame.
8 in the frame + 5 waiting. The total stays the same.
Words to know
- unit price
- the cost for a set amount, like cents per 100 g
- value
- how much you get for your money; better value means more for less
Worked examples
500 g for $4.00 vs 250 g for $2.50
- 1.A: 400 ÷ 5 = 80 c/100 g.
- 2.B: 250 ÷ 2.5 = 100 c/100 g.
= 80 c/100 g (A)
400 g for $3.20 vs 600 g for $4.20
- 1.A: 320 ÷ 4 = 80.
- 2.B: 420 ÷ 6 = 70.
= 70 c/100 g (B)
200 g for $1.80 vs 500 g for $4.00
- 1.A: 180 ÷ 2 = 90.
- 2.B: 400 ÷ 5 = 80.
= 80 c/100 g (B)
For parents
Method: Work out cents per 100 g for each and compare.
What to say: Ask 'which one costs less for the same 100 grams?'
Common mistakes:
- Choosing by the lower total price, not the unit price.
- Answering a pack price instead of the per-100 g rate.