Easy Methods for Quick Number Estimation

Estimation using Rounding

Ever wondered how to quickly check if your calculator answer makes sense? Estimation is the answer! It involves rounding numbers to make calculations easier to do mentally.

Let's see how to estimate the answer to $2123 + 0.00389$ by rounding to 1 significant figure. For $2123$, the first significant figure is 2. Since the second significant figure (1) is between 0-4, we round down to $2,000$. For $0.00389$, the first significant figure is 3. Since the next digit (8) is between 5-9, we round up to $0.004$.

To solve our estimation, we rewrite the equation as $2,000 \div 0.004$. First, we can ignore the decimal point, making it $2,000 \div 4 = 500$. Then we adjust for the decimal place to get our final estimate of $500$.

Quick Tip: When estimating, focus on getting a reasonable approximation rather than an exact answer. This skill will help you quickly spot calculation errors on tests!