1. Starter Round to 1 decimal place
This is the degree of accuracy (how accurate an answer is)
Starter Round to 1 decimal place
5.18
15.09
187.55
90.05
8.97
6.49
Extension: Round to 1 significant figure.
5.2
15.1
187.6
90.1
9.0
6.5 5 20
200 90 9 6
This is also a degree of accuracy

2. To realise that answers in Mathematics are often not exact
Exactly how accurate?
Lesson Objective
To realise that answers in Mathematics are often not exact

3. Key Words Upper Bound Lower Bound Rounding Error (Degree of) Accuracy
The value at which something would be rounded up
Upper Bound
Lower Bound
Rounding Error
(Degree of) Accuracy
Significant figure
Decimal Place
The lowest value something is before rounding
The difference from the exact answer caused by rounding
What something is rounded to

4. Answer these questions
How old are you?
What time is it?
What’s the span of your hand?
What is the value of π?
How many students in this class?
How many students in the whole school?
How accurate are your answers?

5. The time is shown to 2 decimal places
Degrees of Accuracy
Quite often, we see numbers that aren’t exact.
What is the degree of accuracy here?
The time is shown to 2 decimal places

6. Bounds
What is the lowest, and highest, values that this number could be if it is rounded to the nearest ten already? 65
Highest possible value (UPPER BOUND) 60 55
Lowest possible value (LOWER BOUND) 50 60 70

7. Bounds
What is the lowest, and highest, values that this number could be if it is actually rounded to the nearest whole number already?
60.5
Highest possible value (UPPER BOUND) 60
59.5
Lowest possible value (LOWER BOUND) 59 60 61

8. What is the fastest possible time Usain Bolt completed the 100m in?
What is the slowest?
Extension: What would his fastest/slowest speed be? (assume the 100m track is exactly 100m – what would be the effect if it was measured to the nearest meter??)
9.575 seconds
9.585 seconds

9. Rounding Error
So, the exact value of our number could be anything between 59.5 – 60.5 What effect could this have when we come to do some calculations?

10. Effect on calculations
The dimensions are measured to the nearest cm
94.5cm cm
Work out the upper and lower bounds for each dimension
95cm
70cm
69.5cm cm

11. Work out the upper and lower bounds for the perimeter
94.5cm cm
Work out the upper and lower bounds for the perimeter
Extension – Work out the upper and lower bounds for the area of the screen
95cm
70cm
69.5cm cm
Perimeter
Upper Bound – 332cm Lower Bound – 328cm
Area
UB – cm² LB – cm²

12. #harrismaths
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