Decimals and Percentages
What the exam tests
Decimals and percentages tests decimal place value, ordering, the four operations with decimals, and conversion between fractions, decimals and percentages. It also tests percentage of a quantity and simple percentage problems.
Core rules
- In 3.472, the 4 is tenths, the 7 is hundredths and the 2 is thousandths.
- Line up decimal points when adding or subtracting. Multiply as for whole numbers, then count the total decimal places in the factors. Divide by a decimal by making the divisor a whole number.
- To convert a fraction to a decimal, divide the numerator by the denominator. To convert a decimal to a percentage, multiply by 100.
- A percentage is a fraction with denominator 100: 35% = 35/100 = 0.35.
- To find a percentage of a quantity, change the percentage to a decimal or fraction and multiply.
Worked example
Find 15% of MK240. Write 15% as 15/100 = 0.15. Multiply: 0.15 × 240 = 36. So 15% of MK240 is MK36. Check by finding 10% (MK24) and 5% (MK12); their sum is MK36.
Traps that cost marks
Do not write 0.5% as 0.5; it is 0.005. Keep place value when adding decimals: 2.4 + 0.36 = 2.76. Do not confuse 'percentage of' with 'percentage increase'. Remove unnecessary trailing zeros only after the calculation, and make sure the units in a money answer are correct.