Round numbers to a target place value on sight.
A fluency sprint: build the speed and accuracy you need to do this calculation instantly on test day.
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Use three steps:
\(48{,}542\) to the nearest hundred: the hundreds digit is 5 and the next digit is 4, so the answer is \(48{,}500\).
Place names after the decimal point: tenths, hundredths, thousandths. \(10.382\) to the nearest hundredth is \(10.38\).
Watch the carry. When you round up a 9, it becomes 0 and the digit on its left goes up by 1: \(27{,}984\) to the nearest hundred is \(28{,}000\).
Estimates: round each number to the place named, then compute: \(812 \div 41 \approx 800 \div 40 = 20\).
Common slips: looking at all the later digits instead of only the next one, rounding to the wrong place (tens or tenths), cutting digits off instead of rounding, and rounding only one number in an estimate.
Look at the digit right after the hundredths place to decide whether to round up or down: 158.664 rounds to 158.66. Rounding the wrong way gives \(158.67\). Rounding to the nearest tenth instead gives \(158.7\). Rounding to the nearest whole number instead gives \(159\).
Round first: 642 \(\to\) 600, 22 \(\to\) 20. Then \(600 \div 20 = 30\). Rounding only 642 (to 600) and dividing by 22 gives \(27\). Rounding only 22 (to 20) and dividing 642 by it gives \(32\). Rounding 22 the wrong way (to 30) gives \(20\). (Each of these quotients is rounded to the nearest whole number.)
Look at the digit right after the tenths place to decide whether to round up or down: 228.394 rounds to 228.4. Rounding the wrong way gives \(228.3\). Rounding to the nearest hundredth instead gives \(228.39\). Rounding to the nearest whole number instead gives \(228\).