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Rounding and Accuracy

If we round numbers then the accuracy of our calculation can change. The weight of a cooking pot to the nearest kilogram is 7kg. What is the range of possible weights of the pan?

Diagram

Upper and Lower Bounds

You need to know how to use bounds to work the higher and lower bounds of calculations with numbers that have been rounded.

Upper and lower bounds of calculations

Upper and lower bounds of calculations

  • To work out the upper and lower bound of a calculation, you need to work out the upper and lower bound for each value used in a calculation.
  • You can then use these individual bounds to work out the upper and lower bounds of the calculation.
Example - multiplication

Example - multiplication

  • You are calculating the upper and lower bounds of the area of a rectangle.
  • The height is 0.5 to 1 decimal place.
    • The height's lower bound is 0.45 and the upper bound is 0.55.
  • The length is 10 to 2 significant figures.
    • The length's lower bound is 9.5 and upper bound is 10.5.
Example cont. - multiplication

Example cont. - multiplication

  • The lower bound for the area is the smallest possible height × the smallest possible length.
    • I.e. 0.45 × 9.5 = 4.275
  • The upper bound for the area is the largest possible height × the largest possible length.
    • I.e. 0.55 × 10.5 = 5.775
Example - division

Example - division

  • You are calculating the upper and lower bounds of the speed = distance ÷ time.
  • A car travels 30 km to 1 significant figure.
    • The lower bound for the distance is 25 km and the upper bound is 35 km.
  • The time is 7 hours to 1 significant figure.
    • The lower bound of the time is 6.5 hours and the upper bound is 7.5 hours.
Example cont. - division

Example cont. - division

  • The lower bound for the speed of the car is the smallest possible distance ÷ the largest possible time.
    • I.e. 25 ÷ 7.5 = 3.33 km/h
  • The upper bound for the speed of the car is the largest possible distance ÷ the smallest possible time.
    • I.e. 35 ÷ 6.5 = 5.38 km/h
Jump to other topics
1

Number

1.1

Using Numbers

1.2

Fractions, Decimals & Percentages

1.3

Powers & Roots

1.4

Accuracy

2

Algebra

2.1

Introduction to Algebra

2.2

Manipulating Algebra

2.3

Proofs & Functions

2.4

Straight Line Graphs

2.5

Common Graphs

2.6

Transformations & Tangents

2.7

Properties of Graphs

2.8

Solving Equations

2.9

Inequalities

2.10

Sequences

3

Ratio

4

Geometry

4.1

Introduction to Geometry

4.2

Triangles & Quadrilaterals

4.3

Transformations

4.4

Circle Basics

4.5

Circle Theorems

4.6

Measurements & Units

4.7

Calculating Area

4.8

Triangle Formulae

4.9

3D Shapes

4.10

Vectors

5

Probability

6

Statistics

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