Why is estimating before you subtract a good idea?
Estimating is important so that you know whether your calculations produce an answer that is close to your estimate.
We all make mistakes -- even when using a calculator.
It's a good idea because
Estimating before you subtract can be a good idea because it helps you get a rough idea of the expected result and allows you to check the reasonableness of your answer. Here's how you can estimate before subtracting:
1. Look at the numbers: Take a moment to examine the numbers you have. Understand their values and magnitude.
2. Round the numbers: Round the numbers involved in the subtraction problem to the nearest ten or hundred, depending on the level of accuracy required. For example, if you have 87 and 45, you can round them to 90 and 50, respectively.
3. Perform the estimation: Subtract the rounded numbers. In our example of 90 - 50, the estimated answer would be 40.
4. Compare the estimation: Compare the estimate to the numbers you started with. In this case, 40 is reasonably close to the actual result of 87 - 45, which is 42. This indicates that your calculation is likely to be correct.
By estimating before you subtract, you can quickly assess if your answer is in the right ballpark and catch any glaring errors. Estimating is especially useful for mental math and in situations where you need a quick approximation rather than an exact answer.