1. Form 1 Mathematics Chapter 5

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

3.  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.

4.  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 ( 十分位 )  Rounding off to nearest unit ( 個位 )  Rounding off to nearest ten digit ( 十位 )

5.  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

6.  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)

7.  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

8.  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.

9.  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

10.  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.

11.  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

12.  Lesson  Get ready all the time!  Desk  Be order all the time!  Extra Tutorial  Final examination less than 50

13. Enjoy the world of Mathematics! Ronald HUI