Estimation is finding an answer that is close to the exact answer without doing the exact calculation. We use estimation when we need a quick, reasonable answer or to check if our exact answer makes sense.
Estimation gives you a "ballpark" number, not the exact answer. It helps you understand if your final answer is reasonable.
To round to the nearest ten, look at the ones digit. If it is greater than 5, round up. If it is 4 or less, round down.
When rounding to the nearest ten, the number will always end with a zero.
To round to the nearest hundred, look at the tens digit. If it is greater than 5, round up. If it is 4 or less, round down.
When rounding to the nearest hundred, the number will always end with two zeros.
To estimate a sum, first round each number, then add the rounded numbers together.
When estimating sums, always round first, then add. Never add first, then round.
To estimate a difference, first round each number, then subtract the rounded numbers.
When estimating differences, always round first, then subtract. Never subtract first, then round.
Sometimes you need to decide whether to round to the nearest ten or hundred. Think about the numbers and what would make the estimation easiest.
Generally, round to the nearest hundred when numbers are in the hundreds, and to the nearest ten when numbers are smaller.
When solving word problems, first identify what you need to find (sum or difference), then round the numbers appropriately before calculating.
Always read the word problem carefully to understand whether you need to estimate a sum or a difference.