Lesson 5: Add and Subtract Decimals6.NOS.3

I can…

I can add and subtract decimals by lining up the place values and the decimal points.

Key words

• Decimal — A number with a dot, like 0.5, that shows a part less than one.
• Place value — What a digit is worth based on where it sits in a number.
• Tenths — The first spot after the decimal point. It shows parts out of 10.
• Hundredths — The second spot after the decimal point. It shows parts out of 100.
• Annex zeros — Adding zeros at the end of a decimal so numbers line up evenly.

Steps

1. The tank has 128.75 liters. A shuttle adds 46.8 liters. I line up the decimal points and annex a zero: 46.80.
2. I add: 128.75 + 46.80 = 175.55 liters.
3. Now the thrusters use 19.35 liters, so I subtract: 175.55 − 19.35 = 156.20.
4. The final fuel level is 156.20 liters. I check with estimation: about 130 + 47 − 19 = 158, which is close, so my answer is reasonable.

Try it

What is 32.6 − 14.85?

Check your answer

17.75

Rewrite as 32.60 − 14.85. Hundredths: 0 − 5 → borrow → 10 − 5 = 5. Tenths: 5 − 8 → borrow → 15 − 8 = 7. Ones: 1 − 4 → borrow → 11 − 4 = 7. Tens: 2 − 1 = 1. Answer: 17.75.

Sentence starter

I know ___ because ___.

Goal: I can explain my steps using the words decimal, place value, tenths, hundredths, and add zeros.