Substitution
Substitution
When we replace a letter with a value it is
called substitution.
Here are five expressions.
Key Words
Substitute
Evaluate
Evaluate these expressions when a = 5, b = 2 and c= -1.
1) a + b + c
2) 3a + 2c
3) a(b + c)
4) abc
2 – a
c
5) b
What is the
value of each
of these
expressions if
n=8
8
What is the
value of each
of these
expressions if
n = -3
-3
Answers
What is the
value of each
of these
expressions if
n=8
8
What is the
value of each
of these
expressions if
n = -3
-3
When we replace a letter with a value it is
called substitution.
Work out the value of these expressions
when:a = -2
b=5
c=8
i)
ii)
iii)
iv)
b+5=
c–b=
ab =
3b + 2 =
v)
vi)
5(a + b)=
7b =
4
vii) (a+2b)(c-4)
Plenary
Return to your 5 expressions. Attempt the ones you
could not do at the start
Evaluate these expressions when a = 5, b = 2 and c =1.
1) a + b + c
2) 3a + 2c
What does
substitution
mean?
3) a(b + c)
4) abc
Can you write your own statement?
2 – c
a
5) b
Substitution is ……………………………
This is a magic square. Work
out the magic number when:1)
2)
3)
a = 8, b = 3 and c = 4
a = 10, b = 4 and c = 1
a = 14, b = 9 and c = 2
Title
Date
To link algebraic and written representations of formulae 10-Jan-21
Expression
Equation
3n + 1 = 10
Term
2n
Which word matches
which star?
Can you explain your
answer?
n+6
Activity Challenge
Once you have worked out the value of each
expression using n = 4 ….. line the n
expression cards up in value from
smallest to largest and write down.
Is there a number that would change the
order of the cards?
Try some different ones to see!
Card Set 1 – Core Expressions
2n
n
5
n+8
n + 10
Multiply n by 2,
then add 1
Multiply n by 10
n2
Halve n.
n take away 5.
n-5
Add 10 to n.
Times n by 2, then
add 1.
Add 12 to n.
Add 1 to n, then
times by 2.
Multiply n by
itself.
Double n.
Times n by 4, then
minus 2.
Take n away from
20.
Divide n by 5.
Add 8 to n
4n - 2
20 - n
n
2n
+
1
2
n + 12 2( n + 1)
5n
Card Set 2 – Explanations in words
10n
Square n.
Copies in white
Times n by 5.
Easier
Harder
40
250
n=5
How many different
expressions can you find to
make the value in the cloud?
Substitution Bingo
Aim: Full House
Grid: 9 Grid
Play: Calculate value
& cross it off
Numbers to Use
•
•
•
•
2
3
30
32
81
4
16
6
25
-2
19
55
-18
7
-8
34
Question
• 3a + 2b = ?
• when a=4 and b=2
Question
• 4a - b = ?
• when a=3 and b=5
Question
• a - 6b = ?
• when a=10 and b=2
Question
• 3a + b = ?
2
• when a=5 and b= -3
Question
• a2 + 5b = ?
• when a=5 and b=6
Question
• (a+b)2 = ?
• when a=7 and b=2
Question
• 2(a-b) = ?
a
• when a=20 and b= -10
Question
• 3a - 2b = ?
• when a= -4 and b=3
Question
• 2a2 = ?
• when a=4
Question
• 3b + 4a - b = ?
• when a=5 and b=7
Question
• (a+2b)x6 = ?
• when a=7 and b= -1
Question
• 0.5a + b = ?
• when a=14 and b= -5
Question
• ¾a + ½b = ?
• when a=20 and b=8
Question
• a2 + b2 = ?
• when a=4 and b=3
Question
• 2a-b = ?
b
• when a=5 and b=2
Question
• a3 = ?
• when a= -2
In today’s lesson I substituted
values into expressions.
Substitute means ……………..
An example of this is ……………..