Step by step
The question
Question: find the mass when the density is 8.9 g/cm³ and the volume is 25 cm³.
1 Write the rule
The rule: density is the mass divided by the volume.
Density tells us how much mass there is in 1 cm³.
So its unit is g per cm³.
2 Put the numbers in
The density is 8.9.
The volume is 25.
The mass is what we want: we call it m.
Careful!
The mass goes on the top.
The unit, g/cm³, shows it: g on the top.
3 Remove the fraction
The bottom number is 25.
Times 25 will remove it.
We multiply both sides by 25, so they stay equal.
25 divided by 25 is 1.
So just m is left.
Write what is left.
Whole numbers first: 25 times 89 is 2225.
Then 1 decimal place.
So 25 times 8.9 is 222.5.
Let's swap the two sides, so m is on the left.
So m = 222.5.
4 Check
Let's check: 222.5 divided by 25 is 8.9.
That is the density.
So the answer is right!
So the mass is 222.5 g.
Let's look back.
First: write the rule.
Then: put the numbers in.
Then: remove the fraction.
Last: check.