Rounding & Significant Figures
Maths: Edexcel IGCSE Higher, topic 1.8.1
Rounding to Decimal Places
Decimal places can be written as d.p. What are 8.345 and 8.342 rounded to 2 d.p?
E.G 1: We want only the first 2 decimal places
Look at the next digit along
- If the digit is 5 or more we round up.
- If the digit is 4 or less we round down.
3rd decimal place is 5 so round up
E.G 2: We want only the first 2 decimal places
Look at the next digit along
- If the digit is 5 or more we round up.
- If the digit is 4 or less we round down.
3rd decimal place is 2 so round down
E.G 3: When to include zeros
- If the answer is requested to 2 decimal places there must be 2 decimal places in the answer even if they are zeros.
Significant Figures
The first significant figure of a number is the first digit that isn't 0. What is 0.352 to 2 significant figures? What is 0.001827 to 3 significant figures?
E.G 1: 0.352 to 2 significant figures
E.G 1: Look at the 3rd significant figure
- If the digit is 5 or more we round up.
- If the digit is 4 or less we round down.
E.G 1: 3rd significant figure is 2 so round down
E.G 2: 0.001827 to 3 significant figures
E.G 2: Look at the 4th significant figure
- If the digit is 5 or more we round up.
- If the digit is 4 or less we round down.
E.G 2: 4th significant figure is 7 so round up
Test yourself on Rounding & Significant Figures
Which of these numbers are given to 2 decimal places?
Which of these numbers are given to 3 decimal places?
Which of these numbers are given to 1 decimal place?
What is 7.873 rounded to 2 d.p?
What is 8.899 rounded to 2 d.p?