Each machine costs money once (💰) and then earns something every round (🔁).
Divide the cost by what it earns per round. The answer is how many rounds it takes until the machine has paid for itself (⏱️). Write it into the box.
Check off the machine on the left that is done sooner. Careful - that is often the pricier one, because it earns more each round.
For parents
What does this exercise practice?
Here division is a comparison, not an end in itself. Two numbers that say nothing on their own (price and earnings) are brought onto a common unit by dividing - rounds. That is exactly how price per kilo and speed work later on.
Common pitfalls
The most common mistake is simply checking off the cheaper machine. On its own the price says nothing until you know what the machine earns each round.
How to practice at home
While shopping, compare two packs of the same product - what does 100 g cost in the small one, what in the big one? The bigger pack is not always the better deal.