Decimals Objective: Be able to add, subtract, multiply and divide simple decimal numbers without using a calculator Terms and Conditions: To the best of the producer's knowledge, the presentation’s academic content is accurate but errors and omissions may be present and Brain-Cells: E.Resources Ltd cannot be held responsible for these or any lack of success experienced by individuals or groups or other parties using this material. The presentation is intended as a support material for GCSE maths and is not a comprehensive pedagogy of all the requirements of the syllabus. The copyright proprietor has licensed the presentation for the purchaser’s personal use as an educational resource and forbids copying or reproduction in part or whole or distribution to other parties or the publication of the material on the internet or other media or the use in any school or college that has not purchased the presentation without the written permission of Brain-Cells: E.Resouces Ltd.
It’s a good idea to write in any missing noughts Adding and Subtracting When we add or subtract decimal numbers, we must keep the decimal points in line. Here is an example of adding 2.56 and 0.324 2.56 + 0.324 Keep the decimal points in line Add up keeping the decimal point in line 2.884
Subtracting In the same way, we must keep the decimal points in line when subtracting decimals. Here is an example of subtracting 2.06 and from 3.78 3.78 - 2.06 Take away keeping the decimal point in line Keep the decimal points in line 1.72
Try these 1. 3.67 + 2.12 2. 5.65 + 3.76 3. 0.98 + 3.703 4. 0.088 + 3.17 5. 4.65 - 1.52 6. 6.012 - 2.56 7. 9.801 - 0.09 8. 6.37 - 1.099 = 5.79 = 9.41 = 4.683 = 3.258 = 3.13 = 3.452 = 9.711 = 5.271
Multiplying Decimals The chances are that you will be allowed to a calculator for multiplications like: 2.346 x 7.067 But on the non-calculator paper, sometimes simple divisions like 0.3 x 0.02 cause problems. Here is how to do it…
We can change the decimals into whole numbers by multiplying by 10 This makes it a whole number multiplication that we can do . 3 x 02 x 10 x 100 3 x 2 6 Now, we undo the x 10 x 100 which is x 1000 with ÷1000 6 ÷ 1000 = 0.006
1. . 4 x 3 2. . 3 x 5 3. . 8 x 4 4. . 4 x 7 0.12 0.15 0.32 0.28 5. . 9 x 03 6. . 2 x 1 7. . 3 x 2 8. . 3 x 1 0.027 0.02 0.06 0.03 9. . 02 x 4 10. . 2 x 02 11. . 3 x 12. . 1 x 0.008 0.004 0.09 0.01
Multiply the divided number by the same power of 10 The divisor must be a whole number 0.12 ÷ 0.2 1.2 ÷ x 10 2 x 10 Multiply by the power of 10 that makes it a whole number 6 2 1 . 1 Ans 0.6 Keep decimal points in line
The divisor must be a whole number 0.032 ÷ 0.08 3.2 ÷ x 100 x 100 8 Multiply the divided number by the same power of 10 Multiply by the power of 10 that makes it a whole number Now, the divisor is a whole number and we can divide 4 8 3 . 2 3 Ans 0.4 Keep decimal points in line
Try these 1. 2.4 ÷ 0.2 2. 4.5 0.5 3. 2.1 0.3 4. 0.75 5. 3.75 6. 8.88 0.04 7. 0.034 8. 2.04 0.004 = 12 = 9 = 7 = 1.5 = 7.5 = 222 = 0.17 = 510