Why is my child uncomfortable giving an approximate answer?

Because every math task before this one wanted a single correct number, so approximating reads as giving up. Naming the purpose helps: the estimate is a prediction you make before calculating, so that a wildly wrong exact answer stands out immediately. Framed as a check rather than a lazy answer, most children come round quickly.

Why round first instead of adding and then rounding the total?

Because rounding first is the part you can do in your head. Adding 38 and 41 exactly and then rounding to 80 gives the same answer here but needs the full calculation, which defeats the purpose. The skill is getting a usable number without writing anything down, and that means simplifying before you add, not after.

When should a child be able to do this?

Estimating sums by rounding to the nearest ten belongs to third grade and extends to hundreds and thousands in fourth and fifth. It is one of the few skills that keeps paying out forever, in shopping, in cooking, and in every later calculation where a misplaced digit needs catching before it is handed in.

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Close Enough

Round, then add. About how much?

Grades 3-5 · Estimating sums by rounding

How to play

1Two numbers appear, like 38 + 41.
2Round each to the nearest ten, then add those.
3Choose the estimate. You are not looking for the exact total.
4Build a streak of good estimates.

Try a few

About how much is 38 + 41?
Answer: 80
Round each number on its own, then add the rounded pair. 38 becomes 40 and 41 becomes 40, so the estimate is 40 + 40, which is 80. The exact total is 79, so the estimate is one out, and one out is a fine result. The purpose is to know roughly where the answer lives before doing the real sum, not to produce the real sum by a different route.
About how much is 67 + 24?
Answer: 90
Here the two numbers move in opposite directions: 67 rounds up to 70 and 24 rounds down to 20, giving 90. The exact answer is 91. When one number rounds up and the other rounds down the errors partly cancel, which is why this method stays close. When both move the same way the estimate drifts further, and that is worth knowing rather than worrying about.
About how much is 35 + 35?
Answer: 80
Both numbers sit exactly halfway, both round up to 40, and the estimate is 80. The exact total is only 70. This is the round that catches careful children, because 70 is also one of the buttons on screen, and a child who quietly adds the real numbers will pick it and be marked wrong. They were not bad at arithmetic. They answered a question that was not asked.

Why this game helps

Estimating is the check that catches a wrong answer before it is handed in, and children who never learned it accept whatever the procedure produced, including totals that are obviously impossible. The habit is quick: round both numbers to something friendly, add those, and know roughly where the answer should land. It also takes a specific kind of permission, because a child trained to produce exact answers can find deliberately approximating uncomfortable. Being close on purpose is a mathematical skill, not a failure to be precise.

If your child finds this hard

The usual reason for a wrong answer here is not bad estimating but refusing to estimate. The child adds 38 and 41 properly, gets 79, looks for it, and takes whichever button is nearest. Most of the time that works and hides the problem. Watch for the rounds where the exact total is one of the four choices, which happens when both numbers end in 5, because there the exact answer is offered and marked wrong. If your child is losing only those rounds, the arithmetic is fine and the instruction is what is being skipped.

The second error is rounding both numbers down, usually by chopping off the ones digit, so 38 goes to 30 and 67 goes to 60. Estimates built that way are always too small and drift further as the numbers grow. The question to ask is not what digit do you cross out but which ten is nearer, and the answer to that for 38 is obviously 40. Rounding to the nearest ten is a separate skill worth firming up on its own before estimating leans on it.

Some children resist the whole exercise because they have been taught that exactness is the thing being graded, and being deliberately approximate feels like cheating. Give permission explicitly. After each round this game shows both the estimate and the true total, so use that: point out that the estimate told you the answer was somewhere near 80, which is enough to catch an answer of 8 or 800 instantly. Estimation is the check on exact work, never a replacement for it.

Common questions

Why is my child uncomfortable giving an approximate answer?: Because every math task before this one wanted a single correct number, so approximating reads as giving up. Naming the purpose helps: the estimate is a prediction you make before calculating, so that a wildly wrong exact answer stands out immediately. Framed as a check rather than a lazy answer, most children come round quickly.
Why round first instead of adding and then rounding the total?: Because rounding first is the part you can do in your head. Adding 38 and 41 exactly and then rounding to 80 gives the same answer here but needs the full calculation, which defeats the purpose. The skill is getting a usable number without writing anything down, and that means simplifying before you add, not after.
When should a child be able to do this?: Estimating sums by rounding to the nearest ten belongs to third grade and extends to hundreds and thousands in fourth and fifth. It is one of the few skills that keeps paying out forever, in shopping, in cooking, and in every later calculation where a misplaced digit needs catching before it is handed in.

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