Addingandsubtractingdecimals107
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This document provides instructions for adding and subtracting decimals. It outlines three main rules: 1) line up decimals by adding zeros as placeholders, 2) bring the decimal straight down, and 3) only add or subtract like columns. It demonstrates adding and subtracting decimals through examples like 7.1 + 5.8 + 2.5 and 34 - 1.2. The document also introduces a front-end estimation technique for quickly estimating decimal sums and differences by rounding decimals and adding front-end digits. An example shows using this technique to estimate if three video game prices can be purchased using a $25 gift certificate.
Addingandsubtractingdecimals107
- 2. RULES • LINE UP DECIMALS – If you can not drop a straight line down through your decimals, they are not lined up correctly – Add zeros as placeholders if needed • BRING YOUR DECIMAL STRAIGHT DOWN • ADD OR SUBTRACT AS USUAL
- 3. Add & Subtract like Columns 7.1 + 5.8 + 2.5 = _______ ones RULE: Only add and subtract LIKE columns. 1 7.1 5.8 + 2.5 15 . 4 tenths
- 4. Make The Columns Even 34.5 + 21 + 8.5 RULE: Add zeros to even the columns 34.5 21.0 + 8.5 34.5 21.0 + 8.5
- 5. Make The Columns Even 44.589 + 7.23 + 5 3 decimal 2 decimal columns columns 0 decimal columns 1 1 44.589 7.230 + 5 .000 56.819
- 6. Subtract Similar Columns 34 – 1.2 = _____ ones tenths 34. 0 - 1. 2 32 . 8 33
- 8. FRONT-END ESTIMATION • Adding the numbers in front of the decimals • Rounding the decimal numbers to the nearest whole number • Add the two sums
- 9. EXAMPLE • For your birthday you receive a $25 gift certificate. You want to buy 2 used video games, whose prices are: $8.79, $7.29, $ 7.89 Can you buy all 3 games using the gift certificate? 1. Add the front-end digits $8 + 7 + 7 = $22 2. Estimate the sum of the remaining digits (what is behind the decimal) .79 and .29 are about $1 .89 is about $1 $1 + $1 = $2 3. Add the results. $22 + $2 = $24 The estimated sum is less then $25, so you can buy all 3 with your gift card.