1. Estimation in numbers and measurement
Form 1 Mathematics
Chapter 5
Estimation in numbers and measurement

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

3. Mathematics nearby
In World Cup 2002, the total number of goals is 161. There are 64 matches in total. What is the average number of goals per match?
By calculator, we have
161  64 =
What would you say?
2.515
2.5

4. Estimation 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.

5. Example
In a restaurant, your father ordered a set dinner costing $38, your mother ordered a chef salad costing $23 and you ordered grilled ribs costing $48. How much does your family have to pay for this meal?
$38 + $23 + $48
 $40 + $20 + $50 = $110
Hence, your family has to pay about $110.
Actually, the answer is $109! (very close!)

6. Rounding off a number (四捨五入)
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
Rounding off to nearest unit
Rounding off to nearest ten digit

7. Enjoy the world of Mathematics!
Ronald HUI
Enjoy the world of Mathematics!