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How to compare prices in your head
Bigger packs and multi-buys aren't always cheaper. Compare the same amount of each and you'll know.
Work out the price of one
Divide the pack price by how many are in it, then compare with buying one.
Why it works: Prices only compare for the same amount.
Or make the amounts match
Scale both offers up to the same number of items, then compare the totals.
Why it works: 6 is the smallest number both 2 and 3 go into.
By weight: compare the price per 100 g
Divide each price by how many hundreds of grams you get.
Why it works: A 400 g pack is four lots of 100 g.
Buy 2, get 1 free is a third off
You pay for two and get three, so each costs two thirds of the price.
Why it works: You pay for 2 of every 3, and 1 in 3 is about 33% off.
Try it
Tap a problem to check your answer.
4 for $6: price of one?
= $1.50
3 for $7.50: price of one?
= $2.50
5 for $8: price of one?
= $1.60
6 for $4.20: price of one?
= $0.70
More money math: Tip math · Discounts · Splitting a bill
In Math Daily, Perci asks problems like these: tips, discounts and splitting the bill, alongside fractions and percents.
Common questions
How do I know if a multi-buy is a good deal?
Divide its price by how many you get and compare it with the single price. If you won't use them all, the single item can still be the better buy.
What is a unit price?
The price of one item, or of a set amount such as 100 g or 1 liter, so packs of different sizes can be compared.