1. © Brain-Cells: E.Resources Ltd. All Rights Reserved 24/11/09 www.brain-cells.co.ukwww.brain-cells.co.uk Substitute Numbers for Letters Level 5 Objective: Evaluate an expression by substituting given values for letters Terms and Conditions To the best of the producer's knowledge, the academic content of this presentation 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 support material for NC Level 5 maths and is not a comprehensive pedagogy of all the maths topics designated by the National Curriculum for this level. The copyright proprietor has licensed this presentation as a learning aid and prohibits copying or reproduction in part or whole or the publication of the material on the Internet or other media without the written permission of Brain-Cells: E.Resouces Ltd.

2. © Brain-Cells: E.Resources Ltd. All Rights Reserved 24/11/09 www.brain-cells.co.ukwww.brain-cells.co.uk Here is an algebraic expression 3 + h We cannot evaluate (work out its value) unless we are told the value of h. If we are given this information, we can substitute this value for h like this: 3 + h = 4 4 h Substitute in the value of 4 for the h and evaluate the expression = 7

3. © Brain-Cells: E.Resources Ltd. All Rights Reserved 24/11/09 www.brain-cells.co.ukwww.brain-cells.co.uk 1.f + 2 =7.f + 14 = 2.g + 3 =8.g - 12 = 3.h + 3 =9.h - 6 = 4.4 – f =10.24 – f = 5.7 – g =11.32 – g = 6.5 – h =12.17 – h = If f = 3, g = 5 and h = - 4, evaluate the expressions below:

4. © Brain-Cells: E.Resources Ltd. All Rights Reserved 24/11/09 www.brain-cells.co.ukwww.brain-cells.co.uk 1.f + 2 =57.f + 14 =17 2.g + 3 =88.g - 12 =-7 3.h + 3 =9.h - 6 =-10 4.4 – f =110.24 – f =21 5.7 – g =211.32 – g =28 6.5 – h =912.17 – h =21 If f = 3, g = 5 and h = - 4, evaluate the expressions below:

5. © Brain-Cells: E.Resources Ltd. All Rights Reserved 24/11/09 www.brain-cells.co.ukwww.brain-cells.co.uk Here is another algebraic expression 3b + 2 It means 3 x b + 2, but in algebra, we do not write in the multiplication sign between numbers and letters. If we are told the value of b, we can evaluate it like this: 3b + 2 b = 5 Substitute in the value of 5 for the b and evaluate the expression 3 x 5 + 2 = 15 + 2 = 17

6. © Brain-Cells: E.Resources Ltd. All Rights Reserved 24/11/09 www.brain-cells.co.ukwww.brain-cells.co.uk 1.4a + 5 =7.2b – 4a = 2.2b + 4 =8.2a – b = 3.3c + 14 =9.b + c = 4.18 – 5a =10.b - c = 5.15 – 2b =11.3b + 5c = 6.10 – 2c =12.3a – 2c If a = 3, b = 7 and c = - 4, evaluate the expressions below:

7. © Brain-Cells: E.Resources Ltd. All Rights Reserved 24/11/09 www.brain-cells.co.ukwww.brain-cells.co.uk 1.4a + 5 =177.2b – 4a =2 2.2b + 4 =188.2a – b =- 1 3.3c + 14 =29.b + c =3 4.18 – 5a =310.b - c =11 5.15 – 2b =111.3b + 5c =1 6.10 – 2c =1812.3a – 2c17 If a = 3, b = 7 and c = - 4, evaluate the expressions below:

8. © Brain-Cells: E.Resources Ltd. All Rights Reserved 24/11/09 www.brain-cells.co.ukwww.brain-cells.co.uk 1.a + b =7.c – (b – a) = 2.a + c – b =8.a + 2b = 3.ab – c =9.3c – ab = 4.abc =10.2(a + 5) = 5.bc – 12 =11.c – d = 6.cb ÷ a =12.bd = If a = 2, b = 5, c = 10 and d = - 6, evaluate the expressions below:

9. © Brain-Cells: E.Resources Ltd. All Rights Reserved 24/11/09 www.brain-cells.co.ukwww.brain-cells.co.uk 1.a + b =77.c – (b – a) =7 2.a + c – b =78.a + 2b =12 3.ab – c =09.3c – ab =20 4.abc =10010.2(a + 5) =14 5.bc – 12 =3811.c – d =16 6.cb ÷ a =2512.bd =- 30 If a = 2, b = 5, c = 10 and d = - 6, evaluate the expressions below:

10. © Brain-Cells: E.Resources Ltd. All Rights Reserved 24/11/09 www.brain-cells.co.ukwww.brain-cells.co.uk Substitute Letters for Numbers If b = 3 and h = 4, evaluate: 4b – 2h A review sheet covering this presentation is available from www.brain-cells.co.uk