Study guide: Round and Calculate with Place Value
Round to tens and hundreds, compute within 1000, and multiply tens.
Ideas to explain in your own words
- Rounding to a ten compares the two neighboring multiples of ten.
- Hundred rounding compares neighboring multiples of one hundred.
- Exact addition and subtraction depend on matching place values and recording exchanges accurately.
- A multiple of ten contains a whole number of tens.
Useful vocabulary
- round
- Choose a nearby specified place-value landmark.
- estimate
- An approximate result used to assess reasonableness.
Watch your reasoning
- A rounded number is approximate; it does not change the original exact count.
- An answer to hundred rounding must be a full multiple of one hundred.
- A plausible estimate does not prove every digit of an exact answer.
- Forty-two tens is 420, not 42.
A worked review example
Round 263 to the nearest ten. Its neighbors are 260 and 270; distances are three and seven. The nearer landmark is 260. An exact value of 265 would be halfway and round to 270 under the stated convention. Identify both neighboring tens, not only the smaller one. A rounded number is approximate; it does not change the original exact count. Mark the value between its two neighboring multiples of ten.
Make a practice plan
- Round to the Nearest Ten Using Distance: Round 378 and 385 to tens. Expected: 380 and 390.
- Round to the Nearest Hundred: Round 549 and 550 to hundreds. Expected: 500 and 600.
- Check Exact Multi-Digit Calculations with an Estimate: Find 468+257 and check with subtraction. Expected: 725; 725−257=468.
- Multiply Tens as Groups of Ten: Find 9×80. Expected: seventy-two tens, or 720.