Approximation & estimation · Ages 12–13
Rounding up and rounding down
Up: anything left, go up one; down: drop the rest.
How to do it
Method
Up: anything left, go up one; down: drop the rest
3.41: up 3.5, down 3.4, off 3.4 (1 d.p.)
Another way
The mark right or left
3.41 is between 3.4 and 3.5: up takes 3.5, down 3.4
In full
Rounding up: if anything at all follows the place you keep, that place goes up by 1, however small the rest: 3.41 rounded up to 1 d.p. is 3.5. Rounding down: drop everything after it, and the place stays: 3.49 rounded down to 1 d.p. is 3.4. Only rounding off looks at whether the next digit is 5 or more. An exact number stays put all three ways: 3.400 rounded up to 1 d.p. is still 3.4. All three work for place values, decimal places and significant figures. The situation chooses: buses are rounded up (the people left over need a bus too), full boxes rounded down (a box not full doesn't count). Or picture a number line: rounding up takes the mark on the right, rounding down the mark on the left.
Worked examples
Have a go first, then open each one for the answer and the working.
Example 1
30.585 rounded down to 1 decimal place is .
Show the answer and working
Answer: 30.5
Rounding down: everything after the first decimal place goes, however big. So 30.5.
Example 2
0.008688 rounded down to 2 significant figures is .
Show the answer and working
Answer: 0.0086
Count two figures from the first significant one and drop the rest: 0.0086. Only rounding off looks at the next digit.
Example 3
What is 11.300 rounded up to 1 decimal place?
- A. 12
- B. 11.3
- C. 11
- D. 11.4
Choose the right answer
Show the answer and working
Answer: B. 11.3
An exact number stays the same rounded up, down or off: 11.3.
Practice questions to try
Try these 5; the answers are at the end. For a whole worksheet, see VIP worksheets below.
1.45.354 rounded down to 1 decimal place is .
Answer:
2.54,154 rounded down to the nearest hundred is 54,200.
True or false?
Answer:
3.8.715 became 8.8. How was it rounded?
- A. Rounded off to 1 decimal place
- B. Rounded up to 1 decimal place
- C. Rounded up to a whole number
- D. Rounded down to 1 decimal place
Choose the right answer
Answer:
4.0.00379 rounded down to 2 significant figures is .
Answer:
5.92.082 rounded up to 1 decimal place gives the same answer as rounded off to 1 decimal place.
True or false?
Answer:
All the answers
- 1. 45.3
- 2. False
- 3. B. Rounded up to 1 decimal place
- 4. 0.0037
- 5. True
VIP practice notes and papers
Aimed at tests and exams: questions on this topic, new every time, to print or save as a PDF.
- Practice notes: The key point, worked examples step by step, then questions of the same kind to follow, hints fading
- Practice paper: Set out in parts like a school paper, marked, with answers and full working
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