Round to a given place and estimate results of computations.
Free, timed SHSAT practice sets on rounding & estimation— every question includes a full worked explanation, and there's no account required.
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To round, find the place you are rounding to and look at the digit just to its right.
Example: 48,542 to the nearest hundred. The hundreds digit is 5 and the next digit is 4, so the answer is 48,500.
Watch for a carry. 36,951 to the nearest hundred: the next digit is 5, so the 9 hundreds become 10 hundreds, and you get 37,000.
To estimate, round each number to an easy value first, then calculate. \(810 \div 22 \approx 800 \div 20 = 40\).
Common traps:
Look at the digit right after the hundredths place to decide whether to round up or down: 40.430 rounds to 40.43. Rounding the wrong way gives \(40.44\). Rounding to the nearest tenth instead gives \(40.4\). Rounding to the nearest whole number instead gives \(40\).
Multiply the exact values: \(49 \times 22 = 1078\). Rounding both numbers to the nearest ten first (50 and 20) gives \(1000\). Rounding only 49 (to 50) gives \(1100\). Rounding only 22 (to 20) gives \(980\).
Round first: 508 \(\to\) 500, 53 \(\to\) 50. Then \(500 \div 50 = 10\). Rounding only 508 (to 500) and dividing by 53 gives \(9\). Rounding 53 the wrong way (to 60) gives \(8\). Rounding 508 the wrong way (to 600) gives \(12\). (Each of these quotients is rounded to the nearest whole number.)