Estimating products means finding an answer that is close to the exact product. We use rounding or compatible numbers to make multiplication easier to do mentally.
An estimate is not the exact answer, but it helps you check if your exact answer makes sense.
Estimation helps you decide if an answer is reasonable before or after you solve a problem. It is useful when you need a quick answer or when exact numbers are not needed.
Use estimation when you are checking work, comparing prices, or planning time and money.
To estimate products, round one or both factors to a number that is easy to multiply, such as a multiple of 10, 100, or a compatible number.
Example: 378 × 42 → 400 × 40 = 16,000
When rounding, look at the digit to the right of the place value you are rounding to. If it is 5 or greater, round up; if it is less than 5, round down.
Compatible numbers are numbers that are easy to multiply mentally. Sometimes using compatible numbers gives a better estimate than rounding.
Choose numbers that make the math simple while keeping your estimate close to the actual answer.
After solving a multiplication problem, use estimation to check if your exact answer is reasonable. If the exact answer is much greater or smaller than your estimate, recheck your work.
An estimate helps you confirm if your calculation makes sense before moving on to the next problem.