Concept 1 of 5
Multi-Step Money Chains
Today's big idea
Add every cost into one total first, then subtract that total from what you paid.
Working out change before the costs are totalled is where the chain breaks.
How it works
👀 What's going on?
You pick up a few things in a shop, hand over a note, and wait for change. Two different sums are hiding in that moment, and doing them in the wrong order is what goes wrong.
💡 Here's the trick
Look at the receipt above. Every item is costed and added into one total first, and only then is that total taken away from the note you handed over. Change is always the second sum, never the first.
🪄 How to do it
- 1.Work out the cost of each line on the receipt above.
- 2.Add every line into a single total.
- 3.Take that total away from what you paid.
✍️ Try it
Four pens at 15 rupees and a notebook at 40, paid with a 200 note. Then: two books at 65 rupees and three pencils at 12, paid with 300.
The pens come to 60 and the notebook is 40, making 100, so the change is 100 rupees. In the second, 130 plus 36 is 166, so the change is 134 rupees.
⚠️ Watch out
You might be thinking the total is the answer. Very often it is not. Read the last line of the question again. A question ending with how much change wants the subtraction, and the total is only the halfway point.
🌟 Why this matters
Checking your change in a shop is exactly this, and it is the commonest place a real mistake costs real money. Doing the adding first keeps it quick.
Exam tip: Underline whether the question wants the total or the change before you start writing.
Watch me solve one
Quanta solves it
“Watch how I think through one of these — then you try.”
THE PROBLEM
“3 notebooks at ₹45 and a pen at ₹25. You pay with ₹500. What change do you get?”
- 1
Cost of each item
Notebooks = 3 × 45 = ₹135. Pen = ₹25. 🧾
- 2
Add for the total
135 + 25 = 160
- 3
Subtract from what you paid
500 − 160 = 340
- 4
Change ✓
Change = ₹340
Now you try one — same steps, different story 👇
See it in action
⚡ Time to play!
Add every cost first, then subtract the total from the money paid.
BILL · ROUND 1 OF 3
3 pens at ₹12, pay ₹50
How much change?
Quick check
✅ VERIFICATION
You bought 3 items at 20 rupees each and got 40 rupees change. What note did you pay with?
⚡ Finish the activity above first to answer.
Keep going!
Up next: Work-Backwards Puzzles
Spent → add it back. Doubled → halve it.