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Rounding, Estimation & Bounds (Edexcel IGCSE Maths A)

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  • FrontRounding & Estimation

    When rounding a number to the nearest 100, which place value column determines how it rounds?

    E.g. Round 14, 578 to the nearest 100

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  • When rounding a number to the nearest 100, which place value column determines how it rounds?

    E.g. Round 14, 578 to the nearest 100

    When rounding a number to the nearest 100, the digit in the tens place value column determines how the number rounds.

    E.g. When rounding 14, 578 to the nearest 100, the 7 in the tens column tells you to round up to 14, 600

  • How do you find the first significant figure of a number?

    The first significant figure of a number is the first non-zero digit of the number when reading from left to right.

    For example, the first significant figure of 0.457 is 4.

  • True or False?

    The second significant figure of 4.0051 is 5.

    False.

    The second significant figure of 4.0051 is 0.

    The number 0 can be a significant figure as long as there are non-zero values on either side of it.

  • How do you round a number to three significant figures?

    E.g. Round 40, 529 to 3 s.f.

    To round a number to three significant figures:

    1. Find the third significant figure

    2. Check the digit to its right (the fourth significant figure)

      1. If this is 0, 1, 2, 3 or 4 then keep the third significant figure the same and fill the remaining place values with 0s

      2. If it is 5, 6, 7, 8 or 9 then round the third significant figure up to the next value and fill the remaining place values with 0s

    E.g. The fourth significant figure of 40 5329 is 3, this means the third significant figure (5) stays the same and it rounds down to 40 500.

  • What is the general rule for rounding when performing estimating a calculation?

    E.g. Estimate the calculation fraction numerator 2.1 cross times 3.7 over denominator 0.9 end fraction

    When estimating a calculation, the general rule is to round each number to 1 significant figure first.

    E.g. For the calculation fraction numerator 2.1 cross times 3.7 over denominator 0.9 end fraction, round to fraction numerator 2 cross times 4 over denominator 1 end fraction equals 8

  • If you round both numbers up when estimating an addition, will the answer be an overestimate or an underestimate?

    If you round both numbers up in an addition, the answer will be an overestimate.

    E.g. Estimate the calculation 288 + 962.
    Each value rounds up to 1 significant figure, 300 + 1000 = 1300.
    (This gives an overestimate 288 + 962 = 1250).

  • If you round both numbers down when estimating a multiplication, will the answer be an overestimate or an underestimate?

    If you round both numbers down in a multiplication, the answer will be an underestimate.

    E.g. Estimate the calculation 621 × 438.
    Each value rounds up to 1 significant figure, 600 × 400 = 240 000.
    (This gives an underestimate 621 × 438 = 271 998).

  • True or False?

    If you round both numbers up when estimating a division, the answer be an overestimate?

    False.

    If you round both numbers up when estimating a division, it is not easy to tell as to whether the the answer be an overestimate or an underestimate.

  • True or False?

    When estimating a subtraction, a - b, if a is rounded up and b is rounded down, the result will be an underestimation.

    False.

    When estimating a subtraction, a - b, if a is rounded up and b is rounded down, the result will be an overestimation.

    E.g. Estimate the calculation 487 - 317.
    Rounding each value to 1 significant figure, 500 - 300 = 200.
    (This gives an overestimate 487 -317 = 170).

  • Define the term lower bound.

    The lower bound refers to the smallest value that a rounded number could be.

  • What is an error interval?

    An error interval is a range of values that a rounded number could be.

  • True or False?

    If x is a rounded number, the error interval for x can be written as lower space bound less or equal than x less or equal than upper space bound.

    False.

    If x is a rounded number, the error interval for x can not be written as lower space bound less or equal than x less or equal than upper space bound because x can not be equal to the upper bound.

    Instead, lower space bound less or equal than x less than upper space bound is the correct statement.

  • True or False?

    When a number is rounded to one decimal place, the answer is 4.8.

    The upper bound for this number is 4.85.

    True.

    When a number is rounded to one decimal place, the answer is 4.8.

    The upper bound for this number is 4.85.

  • A number has been rounded to the nearest 10, e.g. 780.

    How do you find the lower and upper bounds for the number?

    A number has been rounded to the nearest 10.

    Halve 10 to get 5.
    Add 5 to the rounded number to get the upper bound.
    Subtract 5 from the rounded number to get the lower bound.

    E.g. 780 has been rounded to the nearest 10.
    10 ÷ 2 = 5
    Upper bound: 780 + 5 = 785
    Lower bound: 780 - 5 = 775

  • What do you need to do to the lower and upper bounds of x to find the lower and upper bounds of 4 x?

    To find the lower and upper bounds of 4 x, you need to:

    • Multiply the lower bound of xby 4 to find the lower bound of 4 x.

    • Multiply the upper bound of x by 4 to find the upper bound of 4 x.

  • Which bounds for a and b should you use to find the lower bound of a plus b?

    To find the lower bound of a plus b, you should use the lower bounds of a and b.

  • Which bounds for a and b should you use to find the upper bound of a minus b?

    To find the upper bound of a minus b, you should use the upper bound of a and the lower bound of b.

  • True or False?

    To find the upper bound of a over b, you should use the upper bound of a and the upper bound of b.

    False.

    To find the upper bound of a over b, you should use the upper bound of a and the lower bound of b.

  • True or False?

    To find the lower bound of a b, you should use the lower bound of a and the lower bound of b.

    True.

    To find the lower bound of a b, you should use the lower bound of a and the lower bound of b.

  • The upper bound of x is 3.142345.

    The lower bound of x is 3.141871.

    What level of accuracy should you use to round x to?

    Round x to 4 significant figures (3.142) because both the upper and lower bounds agree as far as 4 significant figures.

Previous:Fractions, Decimals & PercentagesNext:Surds

    1. Topic 1

      Number Toolkit

    2. Topic 2

      Set Notation & Venn Diagrams

    3. Topic 3

      Prime Factors, HCF & LCM

    4. Topic 4

      Powers, Roots & Standard Form

    5. Topic 5

      Fractions

    6. Topic 6

      Percentages

    7. Topic 7

      Compound Interest & Depreciation

    8. Topic 8

      Fractions, Decimals & Percentages

    9. Topic 9

      Rounding, Estimation & Bounds

    10. Topic 10

      Surds

    11. Topic 11

      Using a Calculator

    12. Topic 12

      Ratio Toolkit

    13. Topic 13

      Ratio Problem Solving

    14. Topic 14

      Exchange Rates & Best Buys

    15. Topic 15

      Direct & Inverse Proportion

    1. Topic 1

      Algebra Toolkit

    2. Topic 2

      Algebraic Roots & Indices

    3. Topic 3

      Expanding Brackets

    4. Topic 4

      Factorising

    5. Topic 5

      Completing the Square

    6. Topic 6

      Algebraic Fractions

    7. Topic 7

      Rearranging Formulas

    8. Topic 8

      Algebraic Proof

    9. Topic 9

      Solving Linear Equations

    10. Topic 10

      Solving Quadratic Equations

    11. Topic 11

      Solving Inequalities

    12. Topic 12

      Simultaneous Equations

    13. Topic 13

      Forming & Solving Equations

    1. Topic 1

      Sequences

    2. Topic 2

      Functions

    3. Topic 3

      Coordinate Geometry

    4. Topic 4

      Linear Graphs y = mx + c

    5. Topic 5

      Graphs of Functions

    6. Topic 6

      Estimating Gradients

    7. Topic 7

      Real-Life Graphs

    8. Topic 8

      Graphing Inequalities

    9. Topic 9

      Transformations of Graphs

    10. Topic 10

      Differentiation

    1. Topic 1

      Standard & Compound Units

    2. Topic 2

      Angles in Polygons & Parallel Lines

    3. Topic 3

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    4. Topic 4

      Circle Theorems

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      Area & Perimeter

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      Circles, Arcs & Sectors

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      Volume & Surface Area

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      Congruence, Similarity & Geometrical Proof

    9. Topic 9

      Area & Volume of Similar Shapes

    10. Topic 10

      Right-Angled Triangles - Pythagoras & Trigonometry

    11. Topic 11

      Sine, Cosine Rule & Area of Triangles

    12. Topic 12

      3D Pythagoras & Trigonometry

    1. Topic 1

      Vectors

    2. Topic 2

      Transformations

    1. Topic 1

      Statistics Toolkit

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      Combined & Conditional Probability