Different pack sizes: compare the price for the same quantity
By Erik Nilsen · Kroni3 min read
Two bottles may have different prices because they contain different quantities. The lowest price tag alone cannot tell you which quantity is cheaper. Choose one comparison unit and convert both bottles to it before your child decides.
Use an amount your child can picture
In a hypothetical example, your child considers glue for an optional personal project. A bottle containing 100 millilitres costs 24 units. A bottle containing 250 millilitres costs 50 units. The family has checked that both suit the same use. The prices are arbitrary teaching numbers and do not describe necessary school expenses.
The small bottle costs 24 units per 100 millilitres. The large bottle contains 2.5 times as much. Its price per 100 millilitres is 50 / 2.5 = 20 units. It therefore has a lower quantity price, although the checkout payment is 26 units higher.
Check the answer by comparing 500 millilitres of each. Five small bottles cost 5 × 24 = 120 units. Two large bottles cost 2 × 50 = 100 units. The difference is 20 units for the same quantity, rather than 20 units saved on any possible purchase.
Check the need after comparing
If your child needs only 80 millilitres, the small bottle is enough. Paying 24 units is then the smallest payment covering the actual need, despite the higher quantity price. If there is a concrete need for 250 millilitres, the large bottle is cheaper than three small ones costing 72 units.
A realistic snag is that one bottle may be concentrated or intended for different materials. Volume alone is then not a fair comparison. Read the instructions with an adult and check that the products can meet the same need. This calculation says nothing about whether a glue is suitable.
Let your child draw one box for each 50 millilitres. The small bottle gets two boxes and the large one five. Divide the price between the boxes if the decimal 2.5 is difficult. Each box costs 12 units in the small bottle and 10 in the large one.
Ask your family: “How much do we actually need, and which bottle covers that amount for the smallest payment?” That is a separate question after calculating the quantity price.
Carry the calculation into your family agreement
Kroni can keep track of your child's virtual balance. The app does not transfer money, so any actual purchase is paid for outside it. Agree on what you will record, then check the amount with your child afterwards. Do not deduct a possible cost as though the purchase had already happened. Read about allowance in Kroni.
