Decimals to three places
Solve problems involving numbers with up to three decimal places
What a learner can do afterwards
- Calculate the total of three measurements: 1.234 m + 0.567 m + 2.199 m
- A bottle holds 1.5 litres and 0.375 l is poured out. How much remains?
- Find two numbers with 3 d.p. that add to make 1
1 · Read
Numbers like 1.234 have three digits after the decimal point: tenths, hundredths, and thousandths. You already know how to compare these numbers. Now you'll add and subtract them, just like whole numbers, but the decimal points must line up first. As with whole numbers, 10 of one place make 1 of the next place to the left: 10 thousandths make 1 hundredth, and 10 hundredths make 1 tenth. That is what lets you carry and regroup.
Add 0.755 m, 1.230 m, and 2.015 m. Line up the decimal points so tenths sit under tenths, hundredths under hundredths, and thousandths under thousandths. Adding column by column gives exactly 4.000 m.
Work out 2.4 - 0.615. Write 2.4 as 2.400 so every column lines up. Regroup: 2.400 becomes 1 one, 13 tenths, 9 hundredths and 10 thousandths. Now subtract each column: 10 - 5 = 5 thousandths, 9 - 1 = 8 hundredths, 13 - 6 = 7 tenths, and 1 - 0 = 1 one. The answer is 1.785.
To find a missing part, subtract. What goes with 0.280 to make exactly 1? Write 1 as 1.000 and take away 0.280: 1.000 - 0.280 = 0.720. Then check by adding: 0.280 + 0.720 = 1.000.
Line up the decimal points, padding with zeros if needed, then add or subtract column by column.
All practice questions and readings are original to this dataset. The videos are Khan Academy videos; their terms are not recorded.
2 · Watch
Take it off screen
Where it sits
Learn first
This opens up
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
16 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.