Question

Jam is sold in containers of various sizes shown below.

X=1\4 kg=$3.40
Y=400g =$6.40
Z=1 ½kg=$12.00
Which container of jam represents the best buy? Show all working to explain your answer.​

Answer 1

Z: 1.5 kg for $12

Explanation:

You want the best buy among the choices ...

• 1/4 kg for $3.40
• 400 g for $6.40
• 1.5 kg for $12

Graph

We know that 400 g = 0.40 kg, so we can plot these points on a graph:

(mass, cost) = {(0.25, 3.40), (0.40, 6.40), (1.50, 12.00)}

Joining these points to the origin gives a line segment whose slope is the cost per kg. The line with the least slope (farthest to the right) is the one that identifies the lowest price per kg.

Z is the best buy

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Additional comment

You can divide cost by kilograms to find the lowest cost per kilogram. That is done in the second attachment. Size Z has the lowest cost per kilogram at $8/kg.