Question

500ml of milk for 60p 4 litres for £3.20 Which bottle is better value for money?

Answer 1

Answer:

4 liters for £3.20

Step-by-step explanation:

we want to maximize quantity for each unit of money spent. if we use mL and p, we want to maximize mL/p

500 mL = 60 p

divide both sides by 60p to get a mL/p value

500 mL/60 p = 50/6 p ≈ 8.3 mL per pence

4 L = £3.20

note:

1000 mL = 1L

divide both sides by 1 L/ 1000 mL

1000 mL / 1 L = 1

1 L / 1000 mL = 1

100 p = £1

divide both sides by 100p / £1

100p / £1 = 1 = £1 / 100p

convert everything to the same units (mL and p) to accurately compare

4 L = £3.20

4L  = 4L * 1 = 4L * 1000 mL / 1 L = 4000 mL. Note that we have two options to choose from -- 1000 mL / 1 L and 1 L / 1000 mL. We choose the first one here because we want the 4L to cancel out with the 1 L

£3.20 = £3.20 * 1 = £3.20  * 100p / £1 = 320 p. note we put the £1 on the bottom so the euros cancel out.

thus,

4 L = £3.20

= 4000 mL = 320p

divide both sides by 320p to get a mL / p value

4000 mL / 320 p = 12.5 mL/p

8.3 mL per pence in the first one

12.5 mL per pence in the second one

the second one has a higher mL per pence, so that is a better value