Estimating
Estimating means quickly finding an approximate answer by rounding numbers before calculating, giving a result close enough to verify whether an exact answer is reasonable. In Grade 6 Saxon Math Course 1 (Chapter 2: Problem Solving with Number and Operations), students round each number in a problem to its leading place value, then add, subtract, multiply, or divide the rounded values. For Javier buying a $3.85 notebook and a $1.29 eraser: round to $4 + $1 = $5, so $5 is a reasonable estimate. Estimation is also used to check mental arithmetic and to judge if a calculator answer makes sense.
Key Concepts
Property Estimating is a quick way to 'get close' to the answer. To estimate, we round the numbers before we add, subtract, multiply, or divide.
Examples Estimate the sum of 489 and 214: Round to $500 + 200$, which is 700. Estimate the difference of 804 and 496: Round to $800 500$, which is 300. Estimate the product of 38 and 22: Round to $40 \times 20$, which is 800.
Explanation Estimating is your math superpower for getting 'close enough' answers super fast! Instead of dealing with tricky numbers like 467 + 312, just round them to their friendly neighbors first. In this case, 500 and 300. Adding those is a piece of cake! It's perfect for quickly checking if your exact answer is reasonable.
Common Questions
What is estimating in math?
Estimating means finding a quick approximate answer by rounding numbers first, then calculating. The result is close to but not necessarily equal to the exact answer.
Estimate the sum of $3.85 and $1.29.
Round $3.85 to $4 and $1.29 to $1. Estimated sum = $5.
How is estimating useful when checking calculator answers?
Estimate first, then compare to the calculator output. If they differ greatly, a calculation error likely occurred.
Estimate 47 x 19.
Round 47 to 50 and 19 to 20. Estimated product = 50 x 20 = 1,000. Exact answer 893 is close to 1,000.
When should you use estimation instead of an exact answer?
Use estimation when a rough answer is sufficient, such as deciding if you have enough money for a purchase, or for a quick mental check before a detailed calculation.