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JSS2: MATHEMATICS - 1ST TERM

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  1. Properties of Whole Numbers I | Week 1
    4 Topics
    |
    1 Quiz
  2. Properties of Whole Numbers II | Week 2
    4 Topics
    |
    1 Quiz
  3. Properties of Whole Numbers III | Week 3
    5 Topics
    |
    1 Quiz
  4. Indices | Week 4
    2 Topics
    |
    1 Quiz
  5. Laws of Indices | Week 5
    5 Topics
    |
    1 Quiz
  6. Whole Numbers & Decimal Numbers | Week 6
    4 Topics
    |
    1 Quiz
  7. Standard Form | Week 7
    3 Topics
    |
    1 Quiz
  8. Significant Figures (S.F) | Week 8
    4 Topics
    |
    1 Quiz
  9. Fractions, Ratios, Proportions & Percentages I | Week 9
    6 Topics
    |
    1 Quiz
  10. Fractions, Ratios, Proportions & Percentages II | Week 10
    4 Topics
    |
    1 Quiz
  11. Fractions, Ratios, Proportions & Percentages III | Week 11
    3 Topics
    |
    1 Quiz
  12. Approximation & Estimation | Week 12
    1 Topic
    |
    1 Quiz



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Topic Content:

  • Rounding Off Numbers

To round off numbers simply means making a number simpler but keeping its value close to what it was. Rounding numbers means adjusting the digits (up or down) to make rough calculations easier.

The result will be an estimated answer, not a precise one.

For example, if the population of a country is 8, 214, 426 in a certain year, this number is hard to remember but if we say the population of that country is 8 million, it is a good estimate, because it does not make any real difference what the exact number is. For example, 73 is rounded off to 70 because 73 is closer to 70 than 80.

Rules:

1. Round down digits  0, 1, 2,3,4,   (i.e. add 0)

2. Round up digits  5, 6, 7, 8, 9   (i.e. add 1)

To find the number of decimal places, simply count the number of figures after the decimal point.

Decimal places (d.p)

Screenshot 2023 08 20 at 23.15.30

Worked Example 7.3.1:

Write:

a. 17.6536
b. 25.2999 

to 

i. 1 d.p
ii. 2 d.p
iii. 3 d.p

 

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Responses

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Evaluation Questions 1

Answers:

a. \( \scriptsize 9.0785 \: \times \: 10^4 \)

b. \( \scriptsize 2.9560578 \: \times \: 10^7 \)

c. \( \scriptsize 2.87251 \: \times \: 10^2\)

d. \( \scriptsize 2\: \times \: 10^4 \)

e. \( \scriptsize 5.5 \: \times \: 10^4 \)

f. \( \scriptsize 1.07 \: \times \: 10^5 \)

g. \( \scriptsize 7.7 \: \times \: 10^2 \)

h. \( \scriptsize 4 \: \times \: 10^0 \)

 

Evaluation Questions 2

Answers:

a. 6.2

b. 430 000

c. 93 700 000

d. 3 020 000

e. 1 200

f. 152 300

 

Evaluation Questions 3

Answers:

a. \( \scriptsize 5.46 \: \times \: 10^{1} \)

b. \( \scriptsize 3.07 \: \times \: 10^{-4} \)

c. \( \scriptsize 2.75 \: \times \: 10^{-3} \)

d. \( \scriptsize 5.7 \: \times \: 10^{-5} \)

e. \( \scriptsize 1 \: \times \: 10^{-7} \)

f. \( \scriptsize 2.51 \: \times \: 10^{-1} \)

g. \( \scriptsize 2.51 \: \times \: 10^{-2} \)

h. \( \scriptsize 2.51 \: \times \: 10^{-3} \)

i. \( \scriptsize 2.51 \: \times \: 10^{-4} \)

j. \( \scriptsize 2.51 \: \times \: 10^{-5} \)

Evaluation Questions 4

Answers:

a. 0.0043

b. 0.000032

c. 0.000 000 189

d. 0.000 13

e. 0.0308

f.  0.00009

g. 0.000 004

h. 0.0055

Evaluation Questions 5

Answers:

a.
i. 0.1
ii. 0.09
iii. 0.088
iv. 0.0881

b.
i. 25.4
ii. 25.44
iii. 25.440
iv. 25.4400

c.
i. 16.3
ii. 16.27
iii. 16.271
iv. 16.2709

d.
i. 1.0
ii. 1.00
iii. 0.999
iv. 0.9991

Evaluation Questions 6

Answers:

a.
i. 5. 2
ii. 5.25
iii. 5.249
iv. 5.249635

b.
i. 4.0
ii. 4.00
iii. 3.998
iv. 3.998 226

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