Adding & subtracting tenths

Japanese school year: Elementary 3

What you learn

You will learn how to add and subtract decimals with tenths by aligning the decimal points vertically. This technique is useful for combining and comparing fractional measurements of length or liquid volume. Prior mastery of multi-digit whole number addition and subtraction will make this easier.

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Key points

This is the alignment rule for column addition and subtraction of decimals. Line up the decimal points vertically to match each place value, then compute column by column.

This equation shows the relationship between tenths ( $0.1$ ) and whole numbers ( $1$ ). Ten groups of $0.1$ carry over to $1$ , showing that decimals follow base-10 rules just like integers.

10 \times 0.1 = 1

This is the rule for writing the final answer. Place the decimal point in the answer directly below those above, and drop any unnecessary trailing zeros at the end of the decimal part.

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Practice 1Coming soon