Step by step
The question
Question: find the density when the mass is 90 kg and the volume is 3 m³.
Mass 90 kg, volume 3 m³. Find the density.
1 Write the rule
The rule: density is the mass divided by the volume.
density = massvolume
Density tells us how much mass there is in 1 m³.
So its unit is kg per m³.
density = the mass of 1 cm³
unit: kg ÷ m³ → kg/m³
2 Put the numbers in
The mass is 90.
The volume is 3.
d = 903
3 Work it out
Careful!
The mass goes on the top.
The unit, kg/m³, shows it: kg on the top.
Careful: not 390 ✗
90 divided by 3 is 30.
density = 30 kg/m³
So the density is 30 kg/m³.
4 Check
Let's check.
30 in each m³, for 3 m³: 30 times 3 is 90.
That is the mass.
So the answer is right!
30 kg in each m³: 30 × 3 = 90 kg
Let's look back.
First: write the rule.
Then: put the numbers in.
Then: work it out.
Last: check.
Answer
density = 30 kg/m³