Addition of decimals practice

Adding decimals is the same column addition your child already knows, with one new duty: tenths go under tenths and thousandths under thousandths. The decimal point is the guide that keeps them there.

The first row tests that duty right away. In 3.25 + 0.075 the numbers have different lengths, so a child who lines up the right edges adds 5 thousandths to 5 hundredths. Writing 3.250 first, with a placeholder zero, makes the columns match, and the sum becomes 3.325. Later rows carry across the point, as in 85.66 + 12.54 = 98.20, where the hundredths carry into the tenths and the tenths into the ones.

This is 6.NS.B.3 in Grade 6: fluent work with multi-digit decimals using the standard algorithm.

Before any adding, point to 74.492 + 2.109 and ask, "Which digits are the tenths?" Many kids slide 2.109 to the left edge of the box because it looks short, and its 2 ends up under the 7 tens. The points should sit in one straight line.

A quick habit helps: draw a light vertical line through both points before writing anything. Then have your child name each column as they add it. "Thousandths first, then hundredths."

Two bottom sums cross 1,000: 551.260 + 720.952 and 567.132 + 730.413. Ask your child to read 1,272.212 aloud. If they stall at the comma, talk about place value on both sides of the point.

Hand your child a short grocery receipt and cover the total. They line up the prices on grid paper, add them, then uncover the total to see if the store agrees.

At the kitchen scale, read a weight aloud, like 2.375 pounds of apples, and ask for a second one to add. Mixed lengths, like 2.375 and 1.5, are the best practice because they need that placeholder zero.

For a lighter evening, The Grapes of Math by Greg Tang is full of grouping tricks that make adding in the head faster.

Name what they did: "You kept every point in one line, all eighteen times." The next sheet turns the columns around for decimal subtraction, where borrowing across a zero is the new challenge.