2. Rounding and Estimating Create a magic number square This is where every row, column and diagonal add up to the same total. Eg Now design your own to add up to 28 and if you do that try 32. 11310 789 6135

3. To get you mind working.. Brain Gym time!!

4. Objectives for today By the end of the session you will: Approximate numbers to, 1. the nearest 10, 100 2. 1 and 2 decimal places 3. 1 and 2 significant figures Use estimation for size and to check working out.

5. In groups of 2 or 3, decide what the following mean and what is involved in doing it. You have 5 minutes to get your ideas down on paper. 1. Approximating 2. Rounding 3. Estimating

6. Findings….. Approximating Rounding Estimating

7. Why do we need to be able to approximate and estimate? Sometimes we only need an approximate answer to a problem or question. We do not need to be always exact.

8. Working in 2s or 3s. Look at the information on the sheet. You have 10 minutes to create a quick poster to say, What the main rule for rounding is. What you do to round to, The nearest ten and a hundred To 2 decimal places To 2 significant figures

9. Examples Rounding 27 to the nearest ten - Answer 30 Rounding 357 to the nearest hundred – Answer 400 Rounding 2.634 is 2 decimal places - Answer 2.63 Rounding 34.265 to 2 decimal places – Answer 34.27 Rounding 35.54 to 2 significant figures -Answer 36 Rounding 0.0455 to 2 significant figures - Answer 0.046

10. Findings - Recap Main rule – Look at the figure to the right of where you are rounding to. If this number is, 0 to 4 – eg 454 becomes 450 5 to 9 – eg 457 becomes 460

11. Findings Recap– To the nearest 10, hundred and thousand If to 10, your answer should have no decimal points and should end in one zero eg 19 = 20 If to 100, as above but should end in 2 zeros eg 805 = 800 It to 1000, as above but should end in 3 zeros Eg 8950 = 9000

12. Findings recap - Decimal places and significant figures 2 Decimal places We need two numbers after the decimal point, look at the 3 rd number and use the main rule. Eg 36.5823 is 36.58 2 Significant Figures Count all the numbers not just the ones after the decimal point. Always count the numbers from the left. Eg 16.045 is 16

13. You have 10 minutes to answer the questions.

14. Using estimation to check results and quantities Am I bothered???????????????? You should be, it’s very useful as it can help you spot mistakes and you will need it in your assignment.

15. Things to help you estimate Use your white board for your answer 30 cm or 12 inches is the length of a ruler A bag of sugar is 1 kilo or about 2lbs 1/2 litre or 500ml is a small bottle of water

16. Spotting errors – checking your work Using rounding and estimating together! Round the numbers to 1 significant figure and then say if you think the answer is right or wrong. RECAP SIG FIGS 8.67 x 51.9 = 44.9973 33.29 x 3.2 = 106.528 521 divided by 97.6 = 0.5338 7.4 x 4.2 x 0.95 = 29.526

17. Recap of work and objectives By the end of the session you will have: Approximated numbers to, 1. the nearest 10, 100 2. 1 and 2 decimal places 3. 1 and 2 significant figures Used estimation for size and to check working out. Homework – Try it when you are out and spend money, check roughly by estimation. Are you being charged the right amount? Now mark up your progress card and hand your work in.