Problem Solving Example
The Problem:
1.00 gallons of a liquid weighs 23 lbs. What is its density in g/cm3?
1. READ the problem.
Gallons is a volume. lbs is an English force unit that can be converted into a metric mass unit. Density is mass divided by volume. We can do this.
2. LIST all data and other information given. Be sure and put UNITS with all numbers.

Volume of liquid = 1.00 gallons
'mass' of liquid = 23 lb

3. Clearly state WHAT YOU ARE TO SOLVE FOR.

We want density = mass/volume = grams/cm3

4. Write down ways the information is LINKED.

>From Tables we find that:
1 lb = 454 g
1 gal = 3.785 L
1 L = 103 cm3

5. Look at what you have and FIGURE OUT how to solve the problem.

It looks like we have everything we need, but having one quantity divided by another confuses me as to how to set this up. Let's try the Chunk method in step 6.

6. If you are still stuck, break the problem down into smaller CHUNKS.

Chunk 1: What is the grams?
Chunk 2: What is the cm3?

Mass =

Volume =

Density =

7. Do a REALITY CHECK.

The density of water is 1.0 g/cm3. It seems reasonable that another liquid might be 2.8 times as dense.