Mathematics
How to Choose the Right Maths Formula for a Question
BAMIDELE, KAYODE · 28 September 2026
Knowing many mathematics formulas is useful.
But there is another skill that is just as important:
Knowing which formula to use and when to use it.
Many students can remember formulas but still struggle when they meet a question in an examination.
For example, a student may know the formula for the area of a rectangle, the formula for simple interest, and the formula for speed. But when these formulas appear inside word problems, the student may not know which one applies.
Why?
Because solving mathematics isn't just about remembering formulas.
You also need to understand the question.
You need to identify the information you have, determine what you are being asked to find, and then choose a method that connects the information to the required answer.
This article explains a simple approach students can use when they are unsure which maths formula to choose.
---
# Why Knowing Formulas Isn't Enough
Imagine a student memorizes this formula:
Area of a rectangle = length × width
The student knows the formula perfectly.
Now consider this question:
A rectangular classroom is 12 metres long and 8 metres wide. Find the area of the classroom.
The student should immediately recognize that the formula applies.
But mathematics questions are not always written so directly.
A question might contain extra information, different units, or several pieces of information.
For example:
A rectangular school compound has a length of 20 metres and a width of 15 metres. A path measuring 2 metres wide runs along one side of the compound. Find the area of the compound excluding the path.
Now the student has to think more carefully.
The formula itself hasn't changed.
The challenge is understanding what the question is actually asking for.
That is why mathematical problem-solving involves more than memorization.
---
# Step 1: Read the Question Carefully
Before choosing a formula, read the entire question.
Don't immediately start calculating because you recognize a number or a familiar mathematical term.
Ask yourself:
What is this question about?
Is it about:
* Algebra? * Geometry? * Percentages? * Probability? * Statistics? * Simple interest? * Speed, distance and time? * Trigonometry? * Sets? * Mensuration?
Identifying the general topic can narrow down the possible methods.
For example, if the question talks about the distance travelled by a car and the time taken, you may be dealing with the relationship between speed, distance and time.
If it describes the dimensions of a rectangle and asks for the amount of space inside it, you may need an area formula.
The first step is therefore not always calculation.
It is understanding the question.
---
# Step 2: Identify What You Already Know
Once you've read the question, identify the information that has been provided.
For example:
A rectangle has a length of 12 cm and a width of 5 cm. Find its area.
You know:
Length = 12 cm
Width = 5 cm
You also know that the question is asking for the area.
Writing down the information can make the problem much easier to understand.
You could write:
Given:
Length = 12 cm
Width = 5 cm
Find:
Area
Now the appropriate formula becomes much easier to identify.
---
# Step 3: Identify What You Are Trying to Find
This is one of the most useful questions you can ask when solving mathematics:
What exactly am I being asked to find?
Look carefully at the final part of the question.
It might ask you to find:
* Area * Perimeter * Volume * Distance * Speed * Time * Percentage * Profit * Loss * Interest * Mean * Probability * An unknown variable
The answer to this question can help you determine which formula or method to use.
For example:
If you are asked to find area, you should think about the appropriate area formula.
If you are asked to find perimeter, you need a perimeter relationship.
If you are asked to find time, you may need to rearrange the speed-distance-time relationship.
Don't choose a formula simply because you remember it.
Choose it because it helps you find what the question is asking for.
---
# Step 4: Look for Mathematical Clues
Certain words and phrases can give you clues about the mathematical operation or formula you may need.
For example:
### "Altogether"
This may suggest addition or multiplication, depending on the context.
Example:
There are 8 classes with 35 students in each class. How many students are there altogether?
Because the same number occurs for each class:
8 × 35 = 280
---
### "Difference"
This often suggests subtraction.
Example:
What is the difference between 75 and 42?
75 − 42 = 33
---
### "Of"
In percentage questions, "of" can often indicate multiplication.
Example:
Find 20% of 150.
20/100 × 150 = 30
---
### "Per"
This can indicate a rate or a ratio.
Example:
A car travels 120 km in 2 hours. Find its speed.
The relationship involves:
Speed = Distance ÷ Time
---
### "Area"
This tells you to think about an appropriate area formula based on the shape.
For a rectangle:
Area = length × width
For a triangle:
Area = ½ × base × height
The word itself doesn't give you the entire solution, but it helps you identify the type of calculation you need.
---
# Step 5: Match the Information to the Formula
Once you know what is given and what you need to find, think about which formula connects them.
Consider this example:
A rectangle has a length of 12 cm and a width of 5 cm. Find its area.
You have:
Length = 12 cm
Width = 5 cm
You need:
Area
The formula is:
Area = length × width
Therefore:
Area = 12 × 5
Area = 60 cm²
The important thing is not simply remembering:
A = l × w
You should understand why that formula is appropriate for this question.
---
# Example 1: Area of a Rectangle
Let's work through another example.
### Question
A classroom is 10 metres long and 7 metres wide. Find its area.
### Step 1: What do we know?
Length = 10 m
Width = 7 m
### Step 2: What are we finding?
Area.
### Step 3: Which formula applies?
Area = length × width
### Step 4: Substitute the values
Area = 10 × 7
### Step 5: Calculate
Area = 70 m²
### Answer:
70 m²
Notice that the solution wasn't simply about remembering a formula.
The student had to recognize:
Rectangle → Area → Length × Width
---
# Example 2: Simple Interest
Consider another type of question.
A student invests ₦50,000 at 10% simple interest per annum for 2 years. Find the simple interest.
The student needs to recognize that this is a simple interest question.
The formula is:
Simple Interest = P × R × T / 100
Where:
P = Principal
R = Rate
T = Time
So:
P = ₦50,000
R = 10%
T = 2 years
Therefore:
SI = 50,000 × 10 × 2 / 100
SI = ₦10,000
The important skill is recognizing that the information provided matches the simple-interest formula.
---
# Example 3: Speed, Distance and Time
Consider this question:
A bus travels 180 kilometres in 3 hours. Find its average speed.
What do we know?
Distance = 180 km
Time = 3 hours
What are we finding?
Speed.
The relevant relationship is:
Speed = Distance ÷ Time
Therefore:
Speed = 180 ÷ 3
Speed = 60 km/h
Again, the formula becomes easier to identify when you first determine what is given and what you are trying to find.
---
# Step 6: Don't Ignore Units
Units can provide useful clues and can also help you check your answer.
Suppose a question gives:
Length = 12 cm
Width = 5 cm
The area is:
12 × 5 = 60
But the answer isn't simply 60 cm.
Because you are calculating area, the unit becomes:
60 cm²
Similarly:
* Length may be measured in cm or m. * Area may be measured in cm² or m². * Volume may be measured in cm³ or m³. * Speed may be measured in km/h or m/s.
Always pay attention to units.
A calculation can look correct while the final unit is wrong.
---
# Step 7: Check Whether the Formula Makes Sense
After choosing a formula, don't immediately assume you've made the right choice.
Ask:
Does this method actually match the question?
For example, imagine a question asks for the perimeter of a rectangle.
A student remembers:
Area = length × width
and uses it automatically.
The calculation may be mathematically correct, but it answers the wrong question.
For perimeter, the relevant formula is:
Perimeter = 2(length + width)
This is why students should read the question carefully before selecting a formula.
---
# A Common Mistake: Using a Familiar Formula
One common mistake students make is seeing a familiar number or shape and immediately using the first formula they remember.
For example, a student sees a triangle and immediately thinks:
Area = ½ × base × height
But what if the question asks for the perimeter?
The formula for area isn't appropriate.
The lesson is simple:
Don't choose a formula because it looks familiar.
Choose it because it answers the question being asked.
---
# Another Common Mistake: Using Every Number
Some mathematics questions contain information that isn't necessary for the particular calculation.
Students sometimes assume they must use every number they see.
That's not always true.
Suppose a question says:
A rectangular classroom is 12 metres long and 8 metres wide. It contains 40 desks. Find the area of the classroom.
If you're finding the area, the number of desks isn't required.
You need:
Length = 12 m
Width = 8 m
Therefore:
Area = 12 × 8 = 96 m²
The 40 desks are extra information.
Good problem solving involves deciding which information is relevant.
---
# What If You Don't Know Which Formula to Use?
Don't panic.
Getting stuck doesn't mean you cannot solve the question.
Try this process.
### Ask yourself:
1. What topic is this question about?
### Then:
2. What information has been given?
### Then:
3. What am I being asked to find?
### Then:
4. What formula connects the information I have to what I need?
### Finally:
5. Does my answer make sense?
This turns an intimidating question into smaller steps.
---
# Use Your Working to Think Through the Problem
Showing your working isn't only useful for your teacher.
It can help you think.
For example:
Given:
Length = 12 cm
Width = 5 cm
Find:
Area
Formula:
Area = length × width
Substitution:
Area = 12 × 5
Answer:
Area = 60 cm²
When your work is written this way, you can see how you moved from the question to the answer.
If something goes wrong, you can also identify where the mistake occurred.
---
# Check Your Answer
After completing the calculation, stop for a moment.
Ask:
Does my answer make sense?
For example, if a rectangle has a length of 12 cm and a width of 5 cm, an area of 60 cm² makes sense.
But if you somehow get:
6000 cm²
you should pause and check your calculation.
Checking doesn't mean doing the entire question again every time.
It means developing the habit of asking whether your result is reasonable.
---
# What If the Question Requires More Than One Formula?
Some mathematics problems require several steps.
For example, you may need to:
1. Calculate a percentage. 2. Use the result in another calculation. 3. Then determine a final value.
In these situations, don't try to find one formula that solves everything.
Break the question into smaller parts.
Ask:
What do I need to find first?
Then:
What can I calculate using that result?
This makes multi-step problems easier to manage.
---
# Don't Be Afraid to Ask for Help
Sometimes you may understand the question but still not know which formula to use.
That's a normal part of learning.
You can ask your teacher.
You can check your textbook.
You can review a worked example.
You can practise a similar problem.
You can also use an AI Maths Tutor as an additional learning resource.
The important thing is how you use the help.
Don't simply look for the final answer.
Try to understand why a particular formula or method was chosen.
---
# How an AI Maths Tutor Can Help
An AI Maths Tutor can provide additional support when students are working through mathematics questions.
For example, if you don't understand why a particular formula was used, you can study a step-by-step explanation.
Instead of simply asking:
"What's the answer?"
you can focus on questions such as:
"Why did we use this formula?"
or:
"What information in the question tells us to use this method?"
or:
"Can you explain this step?"
This approach keeps the focus on learning.
---
# How Neslern Can Support Step-by-Step Maths Learning
Neslern is an AI-powered maths tutoring platform designed to help students work through mathematics step by step.
Rather than focusing only on the final result, Neslern's approach emphasizes the working behind the answer.
Students can use Neslern to practise mathematics and study worked solutions.
Neslern also supports practice by topic and is designed around mathematics aligned with WAEC, NECO, JAMB and O-Level/IGCSE.
Teaching staff review popular questions, correct them where necessary, and add methods and voice notes.
This gives students another resource they can use when practising or when they need help understanding a mathematical problem.
However, an AI Maths Tutor should be used as a learning aid.
Students should still attempt questions themselves, practise independently and seek guidance from qualified teachers when necessary.
---
# A Simple 5-Step Formula Selection Method
When you're unsure which formula to use, remember:
Read the entire question carefully.
Identify the information you have.
Identify exactly what the question is asking you to find.
Choose the formula or mathematical method that connects the information you have to what you need.
Check your working, units and final answer.
You can remember it as:
READ → IDENTIFY → FIND → CHOOSE → CHECK
This simple process can help you approach unfamiliar mathematics questions more confidently.
---
# Final Thoughts
Choosing the right maths formula is not simply a memory test.
It is a problem-solving skill.
When you face a difficult question, don't immediately search your memory for every formula you know.
Start with the question.
What do I know?
What am I trying to find?
What does each number represent?
Which formula connects what I know to what I need?
Then work through the calculation and check your answer.
Remember:
READ → IDENTIFY → FIND → CHOOSE → CHECK
The more you practise this process, the easier it can become to recognize the right mathematical method.
And when you get stuck, don't just look for an answer.
Understand why the method works.
Use technology as a learning aid, practise independently, and ask your teacher for help when you need it.
### Ready to practise mathematics differently?
Don't just memorize formulas. Understand when and why to use them.
Explore Neslern at neslern.com.
Neslern — Your AI Maths Tutor.
Log in to react to this post.
Frequently asked questions
Stuck on a maths question right now?
Neslern solves it step by step, written the way a real maths teacher would explain it — free to start, no card required.
