How to Add or Subtract Decimals

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Adding and subtracting decimals works like adding and subtracting whole numbers, but the decimal points must be lined up. This keeps tenths with tenths, hundredths with hundredths, and so on.

If one number has fewer decimal places, write trailing zeros so both numbers have the same number of places. Then add or subtract from right to left and bring the decimal point straight down into the answer.

Examples

Example 1: $6.3+2.45=6.30+2.45=8.75$.

Example 2: $10-3.68=10.00-3.68=6.32$.

Practice Exercises

1) Find $3.4+2.1$.

2) Find $7.8-5.3$.

3) Find $0.46+0.32$.

4) Find $6.05+1.7$.

5) Find $9.2-3.86$.

6) Find $12.345+0.655$.

7) Find $15-2.47$.

8) Find $4.008+12.09$.

9) Find $20.3-8.75$.

10) Find $0.9+0.09+0.009$.

11) Find $31.006-4.78$.

12) Find $5.75+6.8-2.125$.

13) A rope is $3.45$ m long and another is $2.875$ m long. What is the total length?

14) A tank has $18.6$ L of water. $7.85$ L is used. How much remains?

15) Find $100.000-0.375$.

16) Find $8.004+0.996$.

17) Find $45.67-(12.8+3.456)$.

18) A runner goes $1.25$ miles, then $0.875$ miles, then $2.6$ miles. How far in all?

19) Find $0.304+12.7-5.089$.

20) A budget has $\$50.00$. Purchases cost $\$12.75$, $\$8.99$, and $\$16.48$. How much money is left?

Answers

1) Line up decimal points: $3.4+2.1$. Add tenths $4+1=5$ and ones $3+2=5$. Answer: $5.5$.

2) Line up decimal points: $7.8-5.3$. Subtract tenths $8-3=5$ and ones $7-5=2$. Answer: $2.5$.

3) Add hundredths: $0.46+0.32=0.78$, because $46+32=78$ hundredths. Answer: $0.78$.

4) Write $1.7$ as $1.70$. Then $6.05+1.70=7.75$. Answer: $7.75$.

5) Write $9.2$ as $9.20$. Subtract $9.20-3.86$. Borrow: $20-86$ hundredths needs regrouping, giving $5.34$. Answer: $5.34$.

6) Line up decimal points: $12.345+0.655$. Thousandths: $345+655=1000$ thousandths, which is $1.000$. So $12.345+0.655=13.000=13$.

7) Write $15$ as $15.00$. Subtract $15.00-2.47=12.53$. Answer: $12.53$.

8) Write $12.09$ as $12.090$. Then $4.008+12.090=16.098$. Answer: $16.098$.

9) Write $20.3$ as $20.30$. Subtract $20.30-8.75=11.55$. Answer: $11.55$.

10) Write all to thousandths: $0.900+0.090+0.009=0.999$. Answer: $0.999$.

11) Write $4.78$ as $4.780$. Subtract $31.006-4.780=26.226$. Answer: $26.226$.

12) Line up decimals: $5.750+6.800=12.550$. Then $12.550-2.125=10.425$. Answer: $10.425$.

13) Add the lengths: $3.450+2.875=6.325$. The total length is $6.325$ m.

14) Subtract the water used: $18.60-7.85=10.75$. So $10.75$ L remains.

15) Borrow across zeros: $100.000-0.375=99.625$. Check: $99.625+0.375=100.000$. Answer: $99.625$.

16) Line up decimal points: $8.004+0.996=9.000$. The sum is $9$.

17) First add inside parentheses: $12.800+3.456=16.256$. Then subtract: $45.670-16.256=29.414$. Answer: $29.414$.

18) Add all distances with aligned decimals: $1.250+0.875+2.600=4.725$. The runner goes $4.725$ miles.

19) First add: $0.304+12.700=13.004$. Then subtract: $13.004-5.089=7.915$. Answer: $7.915$.

20) Add the purchases: $12.75+8.99=21.74$, and $21.74+16.48=38.22$. Subtract from the budget: $50.00-38.22=11.78$. Money left: $\$11.78$.

Free printable Worksheets

How to Add or Subtract Decimals