Every card costs gems. You tell the kinds apart by their shape - circle, triangle, square, diamond.
The row "Price" says what the card costs. The row "Discount" says how much your old cards knock off for good.
Work out price − discount column by column. The result goes into the row "Pay", and on the right everything added up.
If the discount is bigger than the price, you pay nothing for that kind. So 0 - and never less than 0.
Sometimes the price is missing and you only know discount and pay. Then you work backwards - pay + discount.
Example
For parents
What does this exercise practice?
Buying a card practices three or four subtractions side by side without turning them into a worksheet drill - together they answer one single question. The child learns two things. First, that a difference stops at zero - "the discount is bigger" means "I pay nothing", not "I get something back". Second, the reverse - if you know the discount and what is left to pay, you find the price by adding the discount back on. Exactly this back and forth between minus and plus later carries the work with equations.
Common pitfalls
The big stumbling block is a discount that is too big. Something costs 4 gems and you have 6 discount - that is not "minus 2", it is 0. You cannot pay less than nothing; the rest of the discount simply goes to waste. Working backwards, the same case lurks from the other side - if it said "pay 0" there, the price could have been anything from 1 up to the discount, and the task would have many answers instead of one. That is why such tasks are not in the book at all - in a backwards task every column still has something to pay. And one more common mistake - every kind is worked out on its own. A discount on circles does not help one bit with the squares.
How to practice at home
When shopping with a voucher, work it out - what is left to pay? And if the voucher is worth more than the item, you still do not get money back. Or ask it the other way round - it was 3 dollars at the till and the discount was 2 dollars, what did the label say before?
Related: Shopping and adding up prices