Operations with Capacity in Litres for Primary 4

Operations with Capacity in Litres

Performance Objectives

By the end of the lesson, students should be able to:

1. add and subtract in liters;
2. multiply and divide in liters with whole numbers;
3. solve problems on quantitative aptitude related to addition, subtraction, multiplication and division involving liters.

What is Capacity?

Capacity is the amount of liquid a container can hold.

When you pour water into a bottle, the amount of water that fills the bottle up to its brim is the capacity of that bottle. Different containers can hold different amounts of liquid.

Measuring Capacity in Litres

The standard unit for measuring capacity is the litre.

We use the symbol ‘L’ for litres. For example, a bottle of water might hold 1 litre, which we write as 1 L. A larger jerrycan might hold 10 litres, written as 10 L.

Many everyday items are measured in litres. These include:

1. Water in bottles or sachets
2. Milk in cartons
3. Fuel (petrol or diesel) in vehicles
4. Soft drinks in large bottles
5. Cooking oil

Adding Capacity in Litres

When you combine liquids from different containers, you add their capacities together to find the total amount.

Adding capacities in litres is just like adding whole numbers. Make sure to write the unit ‘L’ in your answer.

Worked Example 1: Adding Litres

A bucket contains 5 L of water, and another bucket contains 3 L of water. How much water is there in total?

Solution:

Amount of water in the first bucket = 5 L

Amount of water in the second bucket = 3 L

Total water = 5 L + 3 L = 8 L

There is 8 L of water in total.

Worked Example 2: Adding Litres Vertically

Add 12 L and 7 L.

Solution:

$$
\begin{array}{r}
12 \text{ L} \\
+\quad 7 \text{ L} \\
\hline
19 \text{ L}
\end{array}
$$

The total is 19 L.

Worked Example 3: Adding Multiple Litre Values

A cook used 4 L of oil on Monday, 6 L on Tuesday, and 5 L on Wednesday. How much oil was used in total?

Solution:

Oil used on Monday = 4 L

Oil used on Tuesday = 6 L

Oil used on Wednesday = 5 L

Total oil used = 4 L + 6 L + 5 L = 15 L

The cook used 15 L of oil in total.

Subtracting Capacity in Litres

When some liquid is removed from a container, you subtract to find out how much liquid is left.

Subtracting capacities in litres is like subtracting whole numbers. Remember to write the unit ‘L’ in your answer.

Worked Example 1: Subtracting Litres

A jerrycan has 10 L of petrol. If 4 L of petrol is used, how much petrol is left?

Solution:

Total petrol in jerrycan = 10 L

Petrol used = 4 L

Petrol left = 10 L – 4 L = 6 L

There is 6 L of petrol left.

Worked Example 2: Subtracting Litres Vertically

Subtract 8 L from 25 L.

Solution:

$$
\begin{array}{r}
25 \text{ L} \\
-\quad 8 \text{ L} \\
\hline
17 \text{ L}
\end{array}
$$

The remaining amount is 17 L.

Worked Example 3: Subtracting from a Larger Quantity

A water tank contains 50 L of water. If 15 L is used for washing and 10 L is used for cooking, how much water remains in the tank?

Solution:

Total water in tank = 50 L

Water used for washing = 15 L

Water used for cooking = 10 L

Total water used = 15 L + 10 L = 25 L

Water remaining = 50 L – 25 L = 25 L

There is 25 L of water remaining in the tank.

Multiplying Capacity in Litres

When you have several containers, each holding the same amount of liquid, you can multiply to find the total capacity.

You multiply the capacity in litres by a whole number. The answer will also be in litres.

Worked Example 1: Multiplying Litres

A carton contains 6 bottles of juice, and each bottle holds 2 L of juice. How much juice is in the carton?

Solution:

Capacity of one bottle = 2 L

Number of bottles = 6

Total juice = 2 L $\times$ 6 = 12 L

There is 12 L of juice in the carton.

Worked Example 2: Multiplying Litres Vertically

Multiply 15 L by 3.

Solution:

$$
\begin{array}{r}
15 \text{ L} \\
\times \quad 3 \\
\hline
45 \text{ L}
\end{array}
$$

The product is 45 L.

Worked Example 3: Multiplying Larger Litre Values

A shop bought 8 jerrycans of cooking oil. Each jerrycan holds 20 L of oil. How much oil did the shop buy in total?

Solution:

Capacity of one jerrycan = 20 L

Number of jerrycans = 8

Total oil = 20 L $\times$ 8 = 160 L

The shop bought 160 L of oil in total.

Dividing Capacity in Litres

When you share a total amount of liquid equally among a number of containers or people, you divide to find out how much each receives.

You divide the total capacity in litres by a whole number. The answer will be in litres.

Worked Example 1: Dividing Litres

A 12 L bucket of water is shared equally among 3 children. How much water does each child get?

Solution:

Total water = 12 L

Number of children = 3

Water per child = 12 L $\div$ 3 = 4 L

Each child gets 4 L of water.

Worked Example 2: Dividing Litres Vertically

Divide 48 L by 4.

Solution:

$$
\begin{array}{r}
12 \text{ L} \\
4 \overline{)48 \text{ L}} \\
-\underline{4} \downarrow \\
08 \\
-\underline{8} \\
0
\end{array}
$$

The result is 12 L.

Worked Example 3: Dividing Larger Litre Values

A farmer has 150 L of pesticide to spray on 5 equal sections of his farm. How much pesticide is used for each section?

Solution:

Total pesticide = 150 L

Number of sections = 5

Pesticide per section = 150 L $\div$ 5 = 30 L

Each section uses 30 L of pesticide.

Solving Word Problems with Capacity in Litres

Word problems tell a story using numbers. To solve them, you need to read carefully and decide whether to add, subtract, multiply, or divide.

Worked Example 1: Addition and Subtraction Problem

A shop started the day with 75 L of kerosene. During the day, they sold 30 L and then received another 20 L from a supplier. How much kerosene did the shop have at the end of the day?

Solution:

Starting kerosene = 75 L

Kerosene sold = 30 L

Kerosene remaining after sale = 75 L – 30 L = 45 L

Kerosene received = 20 L

Kerosene at end of day = 45 L + 20 L = 65 L

The shop had 65 L of kerosene at the end of the day.

Worked Example 2: Multiplication and Division Problem

A baker uses 5 L of water for each batch of bread. If the baker makes 4 batches of bread, and then shares the total water used equally among 2 large mixing bowls, how much water is in each bowl?

Solution:

Water for one batch = 5 L

Number of batches = 4

Total water used = 5 L $\times$ 4 = 20 L

Number of mixing bowls = 2

Water in each bowl = 20 L $\div$ 2 = 10 L

Each mixing bowl contains 10 L of water.

Worked Example 3: Mixed Operations Problem

A school buys water in 25 L drums. They bought 3 drums. If 40 L of water was used for drinking and 15 L for washing hands, how much water is left?

Solution:

Capacity of one drum = 25 L

Number of drums = 3

Total water bought = 25 L $\times$ 3 = 75 L

Water used for drinking = 40 L

Water used for washing hands = 15 L

Total water used = 40 L + 15 L = 55 L

Water left = 75 L – 55 L = 20 L

There is 20 L of water left.