Adding & Subtracting Decimals
Line up the decimal points and every digit finds its place; compute from the smallest place
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Line up the decimal points and every digit finds its place; compute from the smallest place
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The decimal column method works just like whole numbers, with one new rule: line up the decimal points. Once the points align, tenths sit over tenths and hundredths over hundredths, so every column adds like with like. The classic mistake is aligning the last digits instead — turning 3.64 + 2.7 into 3.64 + 0.27. Put the two layouts side by side and the error jumps out.
Tap "Next" through every step of the decimal column method: watch the points get aligned (with a dashed guide), compute place by place from the hundredths with carries and borrow dots marked, then compare side by side "points aligned ✓" versus "last digits aligned ✗" to see why the wrong way turns 2.7 into 0.27.