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Rounding Numbers – Part 1

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.

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Rounding Numbers – Part 1

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  1. Rounding Numbers – Part 1 Slideshow 1, Mr Richard Sasaki, Room 307

  2. Objectives • Understand the concept of rounding • Understand the meaning of decimal places, truncation and rounding up • Be able to round numbers up and down

  3. Introduction Welcome 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!

  4. Introduction What’s an easy sounding number close to 9.972? 10 Solving 10 × 3.6 sounds much easier than 9.972 × 3.6. The answer is very close! 10 × 3.6 = 36 There is an 0.1008 inaccuracy. 9.972 × 3.6 = 35.8992 If we don’t have to be perfect, this is fine! However, we need to understand rounding rules. First, let’s look at decimal places.

  5. Decimal Places Look at the decimal number below. 24.9763 4 It has decimal places. 1. Let’s round it to 3 decimal places. 24.9763 is between 24.976 and 24.977. Which is closer? 24.976 2. Let’s round it to 2 decimal places. 24.9763 is between 24.97 and 24.98. Which is closer? 24.98 We round up and down to whatever is closest.

  6. Answers 3 3.28 57.3159 57.32 57 3.3 0.7924 0.79 1 43.2948 43.29 43 3 6.2364 6.24 6 284.3349 284.33 284 4.015 7.2949 7.29 7 4.02 4.0001 4.00 4 4.0 1.9997 2.00 2 (keep the zero!)

  7. Tricky Question A number was rounded to 2 decimal places as below. 24.55 Does this mean that the number must be 24.6 rounded to 1 decimal place? No…it doesn’t. If the number is 24.5 rounded to 1 decimal place, what could it have been? 24.5 1 d.p 24.6 24.549 1 d.p 2 d.p 24.55 Rounding twice (or more) can be bad! It increases inaccuracy.

  8. Truncation Some units can’t be split up, so we truncate. 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.

  9. Rounding Up Sometimes we need to round up. How many 1 litre bottles do we need to hold 3.1 litres? 4 We can’t compress the water! How many 1 litre bottles would 3.1 litres fill? 3 For the next worksheet, we need to decide whether we truncate or round up.

  10. Answers 4 3 2 4 3 Yen 8kg 5 20 178 Yen 5

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