Solving Real-life Measurement Problems

1A plan for every problem

1. Read the question and write down what you know.
2. Change everything into units that fit together.
3. Calculate, one step at a time.
4. Check that the answer makes sense.

Worked example 1: the rainwater tank

The tank is 3 m long, 2 m wide and 1.5 m deep. It is 23 full. How many 20 L jerrycans can be filled from it?

Step 1 volume = 3 × 2 × 1.5 = 9 m³.
Step 2: capacity = 9 × 1 000 = 9 000 L.
Step 3: water in the tank = 23 of 9 000 = 9 000 ÷ 3 × 2 = 6 000 L.
Step 4: jerrycans = 6 000 ÷ 20 = 300 jerrycans.

Worked example 2: how long will it last?

A family uses 60 L of water a day. How many full days will a 1 000 L tank last?
1 000 ÷ 60 = 16 remainder 40. The tank lasts 16 full days, and 40 L are left for the 17th day.

Worked example 3: filling a fish tank

An aquarium is 40 cm long, 25 cm wide and 30 cm high. Keza fills it with a 1.5 L bottle.
Volume = 40 × 25 × 30 = 30 000 cm³ = 30 000 mL = 30 L.
Number of bottles = 30 ÷ 1.5 = 20 bottles.
Mass of the water = 30 kg.

Worked example 4: comparing amounts

Put these amounts of water in order: 1.2 kg of water, 900 mL, 1 500 cm³, 1 dm³.
Write them all in mL: 1 200 mL, 900 mL, 1 500 mL and 1 000 mL.
Order, smallest first: 900 mL, 1 dm³, 1.2 kg of water, 1 500 cm³.

Try it yourself

1. A tank is 2 m long, 1 m wide and 1 m high. How many litres does it hold?
2. How many 5 L buckets are needed to fill a 1 000 L tank?
3. An aquarium is 60 cm × 30 cm × 25 cm. How many litres does it hold?
4. What is the mass of the water in question 3 when the aquarium is full?
5. A family uses 80 L a day. How many days will a full 2 000 L tank last?

Answers

1. 2 × 1 × 1 = 2 m³ = 2 000 L.
2. 1 000 ÷ 5 = 200 buckets.
3. 60 × 30 × 25 = 45 000 cm³ = 45 L.
4. 45 kg.
5. 2 000 ÷ 80 = 25 days.