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Number Trail Grade 5 / Week 05 / Tuesday
2/6
Week 05 · Decimal operations

Tuesday

Subtract decimals
// Add, subtract, multiply and divide to hundredths
⏱ about 15 min

Tuesday: Subtract decimals

Bruce carries a big jug to the fern garden at the next challenge stop.

"This jug holds 2.5 liters of water," he says.

"The ferns need 0.75 liter. How much water will be left in the jug?"

Bennie looks at the numbers and scratches his ear.

"There are no hundredths in 2.5," he says. "So I will write it as 2.50."

"Then I can trade a tenth for ten hundredths, just like trading a ten for ones."

Bruce nods. "Show me how the trades work, and the challenge is yours."

Learn it: line up, then trade

Write 2.5 as 2.50, and line up the decimal points.

Hundredths: 0 - 5 will not work. Trade 1 tenth for 10 hundredths. 10 - 5 = 5.

Tenths: now 4 - 7 will not work. Trade 1 one for 10 tenths. 14 - 7 = 7.

Ones: 1 - 0 = 1.

So 2.50 - 0.75 = 1.75 liters are left.

A jug marked in liters, filled to 1.75 liters
LINE UP AND SUBTRACT
  • Read the question.
  • Tap your answer.
2.5 - 0.75 = ?
6.48 - 2.3 = ?
5.6 - 1.25 = ?
9.05 - 3.4 = ?

Another way: count up

To find 5 - 3.6, start at 3.6 and count up to 5.

From 3.6 to 4 is 0.4. From 4 to 5 is 1.

Add the jumps: 0.4 + 1 = 1.4. So 5 - 3.6 = 1.4.

A number line from 3 to 5 in tenths, with a dot at 3.6
COUNT UP TO SUBTRACT
  • Read the question.
  • Tap your answer.
5 - 3.6 = ?
4 - 1.75 = ?
3.2 - 2.9 = ?
10 - 6.45 = ?
TRAIL STORY PROBLEMS
  • Read the question.
  • Tap your answer.
The trail is 4.2 kilometers long. Bennie has walked 2.75 kilometers. How far is left?
A sunflower is 1.6 meters tall. A daisy is 0.45 meter tall. How much taller is the sunflower?
Bruce has 3 liters of water. He pours 1.25 liters on the ferns. How much is left?
Which addition checks 6.48 - 2.3 = 4.18?
PUT THE DECIMALS IN ORDER
  • Look at the ones, then the tenths, then the hundredths.
  • Tap them from least to greatest.
11st
22nd
33rd
44th
SentenceTrue or false?
2.5 - 0.75 = 1.75?
5 - 3.6 = 2.4?
9.05 - 3.4 = 5.65?
1.2 - 0.5 = 0.7?
WHY THIS EXERCISE5 - 3.6 is 1.4. From 3.6 to 4 is 0.4, and from 4 to 5 is 1.
Try it
Take one long step while a grown-up marks where your heel lands.
Measure the step in meters with a tape measure, like 0.62 meter.
Now take one short step and measure it too.
Subtract to find how much longer the long step is.
Draw a jug with 2.5 liters of water, and show 0.75 liter poured out.

Nice trading! Tomorrow we multiply decimals.

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