Unit 2 · Topic 01 · Operations
The school collected 456 rupees from one class and 3,890 from another.
Anaya wrote them one under the other and added carefully.
She got 4,346. The correct answer was 4,346 too — but only because she had lined them up on the right edge, and she nearly hadn't.
The fundraiser totals came in on scraps of paper and Anaya volunteered to add them up. Class 5A had raised 456 rupees. Class 5B had raised 3,890.
She wrote them down the way they looked tidiest — flush along the left, like a list:
456 on the first line, 3890 on the second, the 4 sitting directly above the 3.
Then she added down the columns. 4 plus 3 is 7. 5 plus 8 is 13. 6 plus 9 is 15. She ended up with something near seven thousand and knew immediately it was wrong, because 456 and 3,890 could not possibly make seven thousand.
Kabir looked over her shoulder. "Your hundreds are sitting on top of their thousands."
Anaya looked again. Her 4 meant four hundred. His 3 meant three thousand. She had been adding four hundred to three thousand as if they were the same size of thing.
She rewrote it, this time lining up the right-hand edge so the ones sat under the ones. The 456 shifted right, leaving an empty space under the 3.
"Fill it with a zero if it helps," said Ms. Rao, passing behind. "0456. It changes nothing about the value and it stops your eye from drifting."
Anaya added again. Ones: 6 plus 0 is 6. Tens: 5 plus 9 is 14 — write 4, carry 1. Hundreds: 4 plus 8 plus the carried 1 is 13 — write 3, carry 1. Thousands: 0 plus 3 plus 1 is 4.
4,346.
"Before you even add," said Ms. Rao, "round them. Five hundred and four thousand is about four and a half thousand. So an answer near seven thousand was never going to be right, and you spotted that yourself."
Anaya wrote 4,346 on the board and, next to it, in small letters, 'check: about 4,500'.
Column addition works because each column holds digits of the same place value. Ones are added to ones, tens to tens, hundreds to hundreds.
So the numbers must be lined up on the RIGHT, not the left. A shorter number is padded on the left with zeros, or simply left blank — never pushed up against the left edge of a longer number.
When a column totals ten or more, only the ones digit of that total is written down and the tens digit is carried into the next column left. That carry is not optional bookkeeping; it is the ten being handed to the place that can hold it.
Estimating first turns addition into something you can check. Round each number, add the round numbers, and you have a rough answer before you start. If the exact result lands far from it, something has gone wrong — usually a misaligned column.
Add up everything your family spent today from the receipts, first by rounding each amount to the nearest ten, then exactly.
Write both answers down. If they are far apart, check your columns before you check your arithmetic.
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