Guide · For JSS 1 – SS 2 students and parents · 6 min read
Percentages in everyday Nigerian life
Fare increases, market discounts, profit and loss, interest and tax: how percentages show up in daily life, how to work each one out step by step, and the traps that catch people out.
By the MathPlug team, Reflex System · Published
Percentages are everywhere once you start looking: a transport fare that goes up, a trader who gives you something off, a bank that pays interest, a receipt with tax added. They are also one of the most common topics in school maths, from JSS 1 right through to WASSCE.
The good news is that almost every percentage question uses one idea: per cent means out of 100. In this guide we take that one idea into the market, the bus park and the bank, with worked examples you can check yourself. All prices and rates here are made-up numbers for practice, not real figures.
Finding a percentage of an amount
To find a percentage of an amount, write the percentage as a fraction out of 100 and multiply. For example, 15% of ₦8,000 = 15100 × 8,000 = ₦1,200.
It also helps to know a few quick ones by heart. You can build almost any percentage from these:
| Percentage | Fraction | Of ₦8,000 |
|---|---|---|
| 50% | 12 | ₦4,000 |
| 25% | 14 | ₦2,000 |
| 10% | 110 | ₦800 |
| 5% | 120 | ₦400 |
| 1% | 1100 | ₦80 |
💡 Tip: To find 15% in your head, find 10% and 5% and add them: ₦800 + ₦400 = ₦1,200. Mental tricks like this are a good way to check a calculator answer.
Percentage increase and decrease
When a price changes, the percentage change compares the change with the original price:
Percentage change = changeoriginal amount × 100%
Suppose (just as an example) the bus fare from Bisi's street to school rises from ₦500 to ₦650. Find the percentage increase. Later it falls from ₦650 to ₦520. Find the percentage decrease.
- Increase = ₦650 − ₦500 = ₦150
- Percentage increase = 150500 × 100% = 30%
- Decrease = ₦650 − ₦520 = ₦130
- Percentage decrease = 130650 × 100% = 20% (divide by ₦650, the price before this change)
A faster way to apply a change is to use a multiplier. A 30% increase means the new price is 130% of the old one, so multiply by 1.3: ₦500 × 1.3 = ₦650. A 20% decrease leaves 80%, so multiply by 0.8: ₦650 × 0.8 = ₦520.
Discounts at the market
A discount is a reduction on the marked price. Ngozi sees a pair of school shoes marked ₦12,000. The seller offers 15% off.
Find the discount and the price Ngozi pays.
- Discount = 15100 × ₦12,000 = ₦1,800
- Price paid = ₦12,000 − ₦1,800 = ₦10,200
- Check with a multiplier: 15% off leaves 85%, and ₦12,000 × 0.85 = ₦10,200.
Real market prices are usually agreed by bargaining, not by percentages. But knowing how to turn "₦1,800 off" into "15% off" helps you compare offers from different sellers quickly.
Profit and loss percent
Traders buy at the cost price and sell at the selling price. Profit or loss percent is always worked out on the cost price, because that is the money the trader put in.
- Profit % = selling price − cost pricecost price × 100%
- Loss % = cost price − selling pricecost price × 100%
Musa buys a basket of tomatoes for ₦25,000 and sells it for ₦30,000. Emeka buys a used bicycle for ₦40,000 and sells it for ₦34,000. Find each percentage profit or loss.
- Musa's profit = ₦30,000 − ₦25,000 = ₦5,000
- Profit % = 500025000 × 100% = 20% profit
- Emeka's loss = ₦40,000 − ₦34,000 = ₦6,000
- Loss % = 600040000 × 100% = 15% loss
Our profit and loss lesson has more practice, including finding the selling price when you know the profit percent.
Simple interest and tax added on
Simple interest is money paid for borrowing or saving, calculated on the original amount (the principal) every year. The formula is I = P × R × T100, where P is the principal, R the rate per cent per year and T the time in years.
Tunde's father saves ₦50,000 at a simple interest rate of 8% per year for 3 years. Find the interest and the total amount.
- I = 50,000 × 8 × 3100
- = 1,200,000100 = ₦12,000
- Amount = principal + interest = ₦50,000 + ₦12,000 = ₦62,000
Some receipts show a tax added on top of the price. Tax rates are set by government and can change, so here we use a made-up rate of 10% just to show the method. On a price of ₦4,500, the tax is 10% of ₦4,500 = ₦450, and the total is ₦4,500 + ₦450 = ₦4,950. Using a multiplier: ₦4,500 × 1.1 = ₦4,950.
Reverse percentages: finding the original price
Sometimes you know the price after a percentage change and need the price before. This is called a reverse percentage, and it is a favourite exam question.
After a 20% discount, a bag costs ₦8,000. What was the original price?
- After 20% off, the customer pays 80% of the original price.
- So 80% of the original = ₦8,000
- Original price = ₦8,000 ÷ 0.8 = ₦10,000
- Check: 20% of ₦10,000 is ₦2,000, and ₦10,000 − ₦2,000 = ₦8,000.
The same idea works for tax. If a total of ₦4,950 includes our made-up 10% tax, then ₦4,950 is 110% of the price, so the price before tax = ₦4,950 ÷ 1.1 = ₦4,500.
Common traps to avoid
- Taking the percentage of the new amount. To remove 10% tax from ₦4,950, do not subtract 10% of ₦4,950 (that gives ₦4,455, which is wrong). Divide by 1.1 instead.
- Thinking up and down cancel out. A ₦500 fare that rises 30% becomes ₦650. If it then falls 30%, it becomes ₦650 × 0.7 = ₦455, not ₦500, because the second 30% is of a bigger number.
- Adding discounts together. 20% off followed by another 10% off is not 30% off. On ₦10,000: ₦10,000 × 0.8 = ₦8,000, then ₦8,000 × 0.9 = ₦7,200. That is ₦2,800 off, which is 28%.
- Dividing by the selling price for profit. Profit and loss percent always use the cost price.
- Forgetting the units. A percentage answer needs the % sign; a money answer needs ₦.
💡 Tip: Before you finish, ask: does my answer make sense? A discounted price must be less than the marked price. An original price found by reverse percentage must be more than the discounted price.
Questions students ask
- How do I calculate percentage increase?
- Subtract the old value from the new value to find the increase, divide by the old value, then multiply by 100. For example, from ₦500 to ₦650 is an increase of ₦150, and 150500 × 100% = 30%.
- Is profit percent calculated on cost price or selling price?
- On cost price. Divide the profit (or loss) by the cost price and multiply by 100.
- How do I find the original price after a discount?
- Work out what percentage of the original is left (for 20% off, it is 80%), then divide the price you paid by that percentage written as a decimal. For example, ₦8,000 ÷ 0.8 = ₦10,000.
MathPlug is not affiliated with WAEC, NECO or any state examination board. Exam details here come from published syllabuses and exam schemes; always check the instructions on your own question paper and your school's timetable. Spotted something to correct? Tell us.