ZIMSEC O Level · Mathematics · Form 1
Fractions, decimals and percentages are three ways of writing the same amount: 1/4 = 0.25 = 25%.
Working with fractions
- To add or subtract, change to a common denominator first.
- To multiply, multiply the numerators and the denominators. Cancel first to keep numbers small.
- To divide, multiply by the reciprocal of the second fraction.
- Change mixed numbers to improper fractions before multiplying or dividing.
Worked example: Calculate 2 1/3 ÷ 1 3/4.
2 1/3 = 7/3 and 1 3/4 = 7/4
7/3 ÷ 7/4 = 7/3 × 4/7 = 4/3 = 1 1/3
Percentages
- To find x% of an amount, multiply by x/100.
- Percentage change = (change ÷ original) × 100.
- To increase by 15%, multiply by 1.15. To decrease by 15%, multiply by 0.85.
Worked example: A bag of mealie-meal costs US$8. The price rises to US$9.20. Find the percentage increase.
Increase = 9.20 − 8 = 1.20
Percentage increase = 1.20 ÷ 8 × 100 = 15%
Exam tip: Percentage change is always worked out on the ORIGINAL amount, not the new one.
Check yourself
- Work out 3/5 + 2/3.
- Write 0.375 as a fraction in its lowest terms.
- A school had 640 learners. Numbers fell by 12.5%. How many learners are there now?
Show answers
- 19/15 = 1 4/15
- 3/8
- 640 × 0.875 = 560
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