Shopkeepers buy by the dozen and sell by the glass. Every decision they make depends on one question — what does a single one cost me? That question is the unitary method, and it is the first thing a Class 6 student needs before profit makes any sense at all.
If you know what many cost, divide to find what one costs. If you know what one costs, multiply to find what many cost.
That is the whole method. The reason it fills a chapter is that everything else — profit, margin, break-even — quietly depends on it. A shopkeeper who does not know their unit cost cannot know whether they made money today.
In a textbook the question ends at “₹4 per lemon” and the child moves on. Nothing depends on the answer being right.
At a real cart, everything does. Get the unit cost wrong and you price below what the glass cost you to make — and you find out at the end of the day when the money is gone. That consequence is what turns a procedure into understanding.
So before sugar, ice, spice or the cup, every glass already owes ₹4. Sell it at ₹3 and you lose money on every single customer — and the busier you are, the more you lose.
In Lemonade Empire your child runs a lemonade cart and uses this exact concept to decide what to buy and what to charge. Free, no signup, plays in a browser.
▶ Play Lemonade Empire free