Form 1 Mathematics Chapter 5
Lesson requirement Textbook 1A Workbook 1A Notebook (and folder) Before lessons start Desks in good order! No rubbish around!
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.
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 Rounding off to nearest tenth digit ( 十分位 ) Rounding off to nearest unit ( 個位 ) Rounding off to nearest ten digit ( 十位 )
Rounding off to nearest tenth digit = 77.2 Rounding off to nearest unit (or one) = 77 Rounding off to nearest ten digit = 80 The actual answer is 77.14
Consider the leftmost digit. Leave the first leftmost digit Other change to 0! E.g = = 68(Actual answer is 77.14)
Consider the “unwanted” digits. All change to 0 Add 1 to left digit next to them E.g Rounding up to nearest tenth digit Rounding up to nearest unit Rounding up to nearest ten digit
Rounding up to nearest tenth digit = 77.3 Rounding up to nearest unit (or one) = 79 Rounding up to nearest ten digit = 110 Actual answer = All are over-estimated.
Consider the “unwanted” digits. All change to 0 Leave all left digits next to them unchanged E.g Rounding down to nearest tenth digit Rounding down to nearest unit Rounding down to nearest ten digit
Rounding down to nearest tenth digit = 76.8 Rounding down to nearest unit (or one) = 74 Rounding down to nearest ten digit = 60 Actual answer = All are under-estimated.
Page 195 of Textbook 1A Class Practice Page 200 of Textbook 1A Questions 3 – 6 Pages of WB 1A Questions SHW (I) Questions 1 - 8
Choose one approximate value which is close in value to all (or most) numbers E.g x 6 =
Choose a pair of numbers which makes the calculation easier E.g 9 9 = E.g x 163 0.25 x 160 = 40
To change the order of the arithmetic operations for easy calculation Only for first x then E.g.
Make some adjustments during or after arithmetic operations E.g.6432 x 7 Consider 6432 x 7 = ( ) x 7 First,6000 x 7 = Then,432 x 7 3000 (400 x 7 = 2800 432 x 7 is close to 3000) So, the answer is about 45000
Page 200 of Textbook 1A Questions 7 – 12 Page 94 of WB 1A Questions SHW (I) Questions
Lesson Get ready all the time! Desk Be order all the time! Extra Tutorial Final examination less than 50 SHW (I) 11 Jan (Fri) OBQ & CBQ Next week
Enjoy the world of Mathematics! Ronald HUI