Skill: Identify relevant information

When a math problem gives you several facts, do not assume you must use every number. First, identify:

• What the question is asking for
• The facts that help find that quantity
• The units for the answer
• Any facts that are extra

Worked example

A school fair has 6 tables. Each table holds 8 bottles of water. Each bottle contains 500 mL of water. The fair lasts 4 hours.

How many bottles of water are on the tables?

Step 1: Find what the question asks

The question asks for the number of bottles.

So, the answer should be measured in bottles, not milliliters or hours.

Step 2: Identify the useful information

The useful facts are:

• There are $6$ tables.
• Each table has $8$ bottles.

These facts tell us how many bottles there are altogether.

Step 3: Identify extra information

The fact that each bottle contains $500\text{ mL}$ is not needed because we are finding the number of bottles, not the amount of water.

The fact that the fair lasts $4$ hours is also not needed.

Step 4: Write an equation

Multiply the number of tables by the number of bottles on each table:

$$6 \times 8 = 48$$

Step 5: Check the answer and units

There are $48$ bottles, so the answer is:

$$\boxed{48\text{ bottles}}$$

The key idea is to use the information connected to the question and leave out numbers that do not help determine the answer.