Average purchase price: count how many items each price covers
By Erik Nilsen · Kroni2 min read
When your child buys the same kind of item at different prices, every item must count in the average. Adding the different price labels and dividing by the number of labels is insufficient. You need the quantities purchased and what each group cost.
Put quantity beside price
In a hypothetical example, your child buys one pen for 20 units and three comparable pens for 12 each. The arbitrary amounts are invented, with equal quality assumed for this exercise.
The first group costs 1 × 20 = 20 units. The second costs 3 × 12 = 36. Four pens therefore cost 56 altogether. The average purchase price is 56 / 4 = 14 units per pen.
Calculating only (20 + 12) / 2 produces 16. That answer gives each price label equal weight, even though three of the four pens cost 12. Check by listing all four prices: 20 + 12 + 12 + 12 = 56.
Use the average for the right question
A practical snag is assuming that a new pen must therefore cost 14. The average describes purchases already made. Check the next price separately. If a fifth pen actually costs 19, the new total becomes 56 + 19 = 75 and the new average is 75 / 5 = 15.
None of the first four prices changes when the average changes. Your child still paid 20 for the first and 12 for each of the next three. Do not replace historical payments with the average in your money record.
Make two columns labelled “actual payment” and “average per item”. The first checks the money; the second summarises this particular collection of purchases.
Ask your family: “How many items sit behind each price, and which question should the average answer?”
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.
