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Rounding rules

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Rounding rules — free printable reference chart

Reference chart

Rounding rules

Which end is it nearer?

  • 4,3004,3504,4004,382Past the middle, so it rounds up to 4,400.
  • 6.46.456.56.47Decimals work the same way: 6.47 is nearer 6.5.
  • 40455043Not yet halfway, so it stays at 40.

The one digit that decides

  • 4,382Rounding to hundreds? Look at the tens digit. 8 is 5 or more, so up.
  • 4,321Same place, different neighbour. 2 is under 5, so the hundreds stay.
  • 297Rounding a 9 up carries, exactly as adding does: 297 becomes 300.

What happens behind it

  • 4,3824,400Whole numbers: the digits behind become zeros, or the number would shrink.
  • 6.476.5After a decimal point they are simply not written.
  • 38 + 5140 + 50 = 90Estimating: round first, then do the easy sum. It is a check, not the answer.
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What's on this chart

Everyone learns "five or more rounds up." Almost nobody is taught the two steps before it, which is where the errors actually happen: finding the place being rounded to, and then looking at the one digit immediately to its right. A child who rounds 4,382 to the nearest hundred by looking at the 2, or by rounding the tens column instead, has applied the famous rule perfectly and still has the wrong answer.

Why this chart helps

The second group answers the question that follows. Rounding 4,382 to the nearest hundred gives 4,400, not 44 — the digits behind the place become zeros rather than disappearing, because the number has to stay the size it was. After a decimal point the opposite is true and they are simply not written, which looks like an inconsistency until you notice that both rules are saying the same thing: keep the value, drop the detail.