Download KS3 Level 5 Substitution - Brain

Substitute Numbers for Letters
Objective: Evaluate an expression by
substituting given values for letters
Level 5
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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:
h=4
3+4
h =7
Substitute in
the value of 4
for the h and
evaluate the
expression
© Brain-Cells: E.Resources Ltd. All Rights Reserved 24/11/09 www.brain-cells.co.uk
If f = 3, g = 5 and h = - 4, evaluate the
expressions below:
1.
2.
3.
4.
5.
6.
f+2=
g+3=
h+3=
4–f=
7–g=
5–h=
7.
8.
9.
10.
11.
12.
f + 14 =
g - 12 =
h-6=
24 – f =
32 – g =
17 – h =
© Brain-Cells: E.Resources Ltd. All Rights Reserved 24/11/09 www.brain-cells.co.uk
If f = 3, g = 5 and h = - 4, evaluate the
expressions below:
1.
2.
3.
4.
5.
6.
f+2=
g+3=
h+3=
4–f=
7–g=
5–h=
5
8
-1
1
2
9
7.
8.
9.
10.
11.
12.
f + 14 =
g - 12 =
h-6=
24 – f =
32 – g =
17 – h =
© Brain-Cells: E.Resources Ltd. All Rights Reserved 24/11/09 www.brain-cells.co.uk
17
-7
-10
21
28
21
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:
b=5
3 x3b
5+2
= 15 + 2
= 17
Substitute in
the value of 5
for the b and
evaluate the
expression
© Brain-Cells: E.Resources Ltd. All Rights Reserved 24/11/09 www.brain-cells.co.uk
If a = 3, b = 7 and c = - 4, evaluate the
expressions below:
1.
2.
3.
4.
5.
6.
4a + 5 =
2b + 4 =
3c + 14 =
18 – 5a =
15 – 2b =
10 – 2c =
7. 2b – 4a =
8.
2a – b =
9.
b+c=
10.
b -c=
11. 3b + 5c =
12.
3a – 2c
© Brain-Cells: E.Resources Ltd. All Rights Reserved 24/11/09 www.brain-cells.co.uk
If a = 3, b = 7 and c = - 4, evaluate the
expressions below:
1.
2.
3.
4.
5.
6.
4a + 5 =
2b + 4 =
3c + 14 =
18 – 5a =
15 – 2b =
10 – 2c =
17
18
2
3
1
18
7. 2b – 4a = 2
8.
2a – b = - 1
9.
b+c= 3
10.
b - c = 11
11. 3b + 5c = 1
12.
3a – 2c 17
© Brain-Cells: E.Resources Ltd. All Rights Reserved 24/11/09 www.brain-cells.co.uk
If a = 2, b = 5, c = 10 and d = - 6, evaluate
the expressions below:
1.
2.
3.
4.
5.
6.
a+b=
a+c–b=
ab – c =
abc =
bc – 12 =
cb ÷ a =
7. c – (b – a) =
8.
a + 2b =
9.
3c – ab =
10.
2(a + 5) =
11.
c–d=
12.
bd =
© Brain-Cells: E.Resources Ltd. All Rights Reserved 24/11/09 www.brain-cells.co.uk
If a = 2, b = 5, c = 10 and d = - 6, evaluate
the expressions below:
1.
2.
3.
4.
5.
6.
a+b=
a+c–b=
ab – c =
abc =
bc – 12 =
cb ÷ a =
7
7
0
100
38
25
7. c – (b – a) =
8.
a + 2b =
9.
3c – ab =
10.
2(a + 5) =
11.
c–d=
12.
bd =
© Brain-Cells: E.Resources Ltd. All Rights Reserved 24/11/09 www.brain-cells.co.uk
7
12
20
14
16
- 30
Substitute Letters for Numbers
If b = 3 and h = 4,
evaluate:
4b – 2h
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© Brain-Cells: E.Resources Ltd. All Rights Reserved 24/11/09 www.brain-cells.co.uk