Topic 14 · Number & Algebra
Decimals & Percentages
Estimation, multiplying and dividing decimals, compound percentage change, reverse percentages and percentage error.
By the end of this topic you can…
- Estimate the answer to a calculation by rounding
- Multiply and divide decimals without a calculator
- Calculate repeated (compound) percentage change
- Find an original amount using reverse percentages
- Calculate a percentage error
Lessons
- Estimating Calculations Rounding every number to one significant figure to get a quick estimate — and using it to catch wrong answers.
- Multiplying and Dividing Decimals Knowing whether an answer will be bigger or smaller, multiplying decimals without a calculator, and dividing by making the divisor a whole number.
- Percentage Change and Compound Interest Using multipliers for percentage increases and decreases, simple versus compound interest, and repeated percentage change.
- Reverse Percentages and Percentage Error Finding the original amount after a percentage change, reversing repeated changes, and measuring how far an estimate or measurement is from the true value.
Decimals and percentages quiz
Twelve questions drawn at random from a bank of eighteen, covering estimation, decimal calculations, percentage change, reverse percentages and percentage error.
12 questions · pass mark 70%