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10. 3D Measurement
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10.04 Units of capacity

Lesson
Practice
Lesson

Are you ready?

Do you remember  units of capacity  ?

Examples

Example 1

What is the appropriate capacity unit to measure a cup of coffee?

This image shows a cup full of coffee and a saucer.
A
\text{L}
B
\text{ML}
C
\text{mL}
Worked Solution
Create a strategy

Use the table of examples below to help you.

ObjectBest unit
Large drop of waterMillilitre
Jug of milkLitre
Apply the idea

A cup of coffee has a small amount of liquid compared to a jug of milk. So a litre is too big.

A mega litre, \text{ ML,} is even larger than a litre, so it would be way too big.

So the correct answer is option C: \text{ mL}.

Idea summary

It is useful to know the capacity of some common objects so that we can estimate the capacity of new objects.

Units of capacity

How do we know which unit of capacity to use?

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Examples

Example 2

Choose the most appropriate unit of measure for finding the amount of water in a dam.

A
Millilitres
B
Megalitres
C
Litres
Worked Solution
Create a strategy

Use the table of examples below to help you.

ObjectCapacity
\text{Glass of water}300\text{ mL}
\text{Carton of milk}2\text{ L}
\text{Water usage per person per day}200\text{ L}
Apply the idea

Dams can store massive amounts of water, enough to supply entire cities. Cities have thousands of people, that each use 200\text{ L} of water per day. So it would need to store millions of litres.

A megalitre is equal to a million of litres. So this is the most appropriate unit.

The correct answer is option B.

Idea summary

A millilitre is about the size of a drop of water.

A litre is about the size of a milk carton.

A megalitre, is a milltion litres, and is about the size of a dam.

Large units for capacity

Let's explore some bigger things to find out more about units for capacity.

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Examples

Example 3

When referring to the capacity of a pool, which of the following could be an appropriate unit to use?

This image shows a rectangular swimming pool.

Select all correct options.

A
\text{mL}
B
\text{L}
C
\text{ML}
Worked Solution
Create a strategy

Think about possible sizes of a pool.

Apply the idea

If we are looking at an olympic size swimming pool which is very large, then we could use megalitres to measure the capacity.

If we lookinf at a kid's pool or a home pool, that's a lot smaller, we could probably use litres to measure the capacity.

The answers are options B and C.

Idea summary

Millilitres can be used to measure the amount of water in a glass.

Litres can be used to measure the amount of water in a large bottle or small pool.

Megalitres can be used to measure the amount of water in a large pool or dam.

Estimate capacity

How can we use things we know to estimate the capacity of larger objects?

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Examples

Example 4

What is the best estimate for the volume of liquid in this container if it is able to hold 1250 \text{ mL} when full?

This image shows a vase with water in it. Ask your teacher for more information.
A
750 \text{ mL}
B
250 \text{ mL}
C
1500 \text{ mL}
D
500 \text{ mL}
Worked Solution
Create a strategy

Compare the two parts of the container.

Apply the idea

The bottom part with water is bigger than the top part without water.

So the volume of the liquid shown is bigger than half of 1250 \text{ mL}, but less than 1250 \text{ mL}.

\displaystyle \dfrac{1}{2} \text{ of }1250\displaystyle =\displaystyle \dfrac{1}{2} \text{ of }1200+\dfrac{1}{2} \text{ of }50Partition 1250
\displaystyle =\displaystyle 600+25Halve 1200 and 50
\displaystyle =\displaystyle 625Add the numbers

From the options we have 750 \text{ mL} which is bigger than 625 \text{ mL} but less than 1250 \text{ mL}.

So option A is the answer.

Idea summary

We use the following units to measure the capacity, or how much something holds, of objects:

UnitAbbreviation
millilitremL
litreL
kilolitrekL
megalitreML

Outcomes

MA3-11MG

selects and uses the appropriate unit to estimate, measure and calculate volumes and capacities, and converts between units of capacity

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