Rounding Numbers – Part 1
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Slideshow 1, Mr Richard Sasaki, Room 307 Rounding Numbers – Part 1
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Rounding Numbers – Part 1. Slideshow 1, Mr Richard Sasaki, Room 307. Objectives. Understand the concept of rounding Understand the meaning of decimal places , truncation and rounding up Be able to round numbers up and down. Introduction. - PowerPoint PPT Presentation
Transcript of Rounding Numbers – Part 1
Slideshow 1, Mr Richard Sasaki, Room 307
Rounding Numbers – Part 1
Objectives• Understand the concept of
rounding• Understand the meaning of
decimal places, truncation and rounding up
• Be able to round numbers up and down
IntroductionWelcome to Grade 9 Maths! Things will be a bit easier for a while. Chapter 1 is always easier than the others.We’ll start by learning about rounding. What’s rounding?Changing a number so it’s easier to work with.Basically, we soften the number. Then its easier to calculate with!
IntroductionWhat’s an easy sounding number close to 9.972?10Solving 10 × 3.6 sounds much easier than 9.972 × 3.6. The answer is very close!
10 × 3.6 = 369.972 × 3.6 = 35.8992If we don’t have to be perfect, this is fine!
There is an 0.1008 inaccuracy.
However, we need to understand rounding rules. First, let’s look at decimal places.
Decimal PlacesLook at the decimal number below.
24.9763It has decimal places.4
1. Let’s round it to 3 decimal places.24.9763 is between 24.976 and 24.977. Which is closer?24.9762. Let’s round it to 2 decimal places.24.9763 is between 24.97 and 24.98. Which is closer? 24.98We round up and down to whatever is closest.
Answers
33.283.33
4.0154.024.0
(keep the zero!)
57.3159 57.32 570.7924 0.79 143.2948 43.29 43 6.2364 6.24 6284.3349 284.33 2847.2949 7.29 74.0001 4.00 41.9997 2.00 2
A number was rounded to 2 decimal places as below. 24.55Does this mean that the number must be 24.6 rounded to 1 decimal place?
Tricky Question
No…it doesn’t. If the number is 24.5 rounded to 1 decimal place, what could it have been?
24.5491 d.p 24.52 d.p 24.551 d.p
24.6Rounding twice (or more) can be bad! It increases inaccuracy.
Some units can’t be split up, so we truncate.
Truncation
What is truncation?Truncation has the same effect as rounding down. We cut off the remainder.Can you think of something in life that we truncate?An example is money. If we divide 89 Yen by 10, we can’t have 8.9 Yen.We remove the 0.9 Yen as it doesn’t make sense. So we are left with 8 Yen.Basically, (to the nearest integer).
Sometimes we need to round up.
Rounding Up
How many 1 litre bottles do we need to hold 3.1 litres? 4We can’t compress the water!
For the next worksheet, we need to decide whether we truncate or round up.
How many 1 litre bottles would 3.1 litres fill? 3
Answers
3
4
8kg
5
5
42
3 Yen
20
178 Yen
