Estimation in numbers and measurement

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Estimationin numbers and measurement

• Form 1 Mathematics
• Chapter 5

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Reminder

• Lesson requirement
• Textbook 1A
• Workbook 1A
• Notebook (and folder)
• Before lessons start
• Desks in good order!
• No rubbish around!

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Estimation (p.189)

• An estimation is a rough guess on the actual
  values.
• It does not represent the real answer.
• In real life, we seldom bring a calculator with
  us. So, we can use estimation to make some
  decisions.
• To get a better estimation, we need some
  techniques to round off a number.

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Rounding off a number (????)

• Consider the unwanted leftmost digit.
• If greater or equal to 5, add 1 to left digit
  next to it.
• Otherwise, leave left digit next to it unchanged.
  
• E.g. 21.29 15.78 30.97 3.24 5.86
• Rounding off to nearest tenth digit (???)
• Rounding off to nearest unit (??)
• Rounding off to nearest ten digit (??)

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Rounding off (????)

• Rounding off to nearest tenth digit
• 21.29 15.78 30.97 3.24 5.86? 21.3
  15.8 31.0 3.2 5.9 77.2
• Rounding off to nearest unit (or one)
• 21.29 15.78 30.97 3.24 5.86? 21
  16 31 3 6 77
• Rounding off to nearest ten digit
• 21.29 15.78 30.97 3.24 5.86? 20
  20 30 0 10 80
• The actual answer is 77.14

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Front-end method (????)

• Consider the leftmost digit.
• Leave the first leftmost digit
• Other change to 0!
• E.g. 21.29 15.78 30.97 3.24 5.86
• 21.29 15.78 30.97 3.24 5.86? 20.00
  10.00 30.00 3.00 5.00 20 10 30 3
  5 68 (Actual answer is 77.14)

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Rounding up (???)

• Consider the unwanted digits.
• All change to 0
• Add 1 to left digit next to them
• E.g. 21.29 15.78 30.97 3.24 5.86
• Rounding up to nearest tenth digit
• Rounding up to nearest unit
• Rounding up to nearest ten digit

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Rounding up (???)

• Rounding up to nearest tenth digit
• 21.29 15.78 30.97 3.24 5.86? 21.3
  15.8 31.0 3.3 5.9 77.3
• Rounding up to nearest unit (or one)
• 21.29 15.78 30.97 3.24 5.86? 22
  16 31 4 6 79
• Rounding up to nearest ten digit
• 21.29 15.78 30.97 3.24 5.86? 30
  20 40 10 10 110
• Actual answer 77.14. All are over-estimated.

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Rounding DOWN (???)

• Consider the unwanted digits.
• All change to 0
• Leave all left digits next to them unchanged
• E.g. 21.29 15.78 30.97 3.24 5.86
• Rounding down to nearest tenth digit
• Rounding down to nearest unit
• Rounding down to nearest ten digit

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Rounding down (???)

• Rounding down to nearest tenth digit
• 21.29 15.78 30.97 3.24 5.86? 21.2
  15.7 30.9 3.2 5.8 76.8
• Rounding down to nearest unit (or one)
• 21.29 15.78 30.97 3.24 5.86? 21
  15 30 3 5 74
• Rounding down to nearest ten digit
• 21.29 15.78 30.97 3.24 5.86? 20
  10 30 0 0 60
• Actual answer 77.14. All are under-estimated.

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Time for Practice

• Page 195 of Textbook 1A
• Class Practice
• Page 200 of Textbook 1A
• Questions 3 6
• Pages 93 - 94 of WB 1A
• Questions 1 - 4
• SHW (I)
• Questions 1 - 8

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Reminder

• Lesson
• Get ready all the time!
• Desk
• Be order all the time!
• Extra Tutorial
• Final examination less than 50

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• Enjoy the world of Mathematics!