C ONSTRUCTING E QUATIONS

Example
A table top measures x cm by y cm. Write down an
expression for its area, A.

Example
The sides of a rectangle are A cm and B cm. Write down an
expression for the perimeter of the rectangle.

Example
A packet of chewing gum holds 8 sticks of gum.
How many sticks are there in
(i)
3 packets
(ii)
8 packets
(iii)
x packets?

Example
A classroom in the new building is designed to hold 35 pupils.
How many pupils can be seated in
(i)
2 rooms
(ii)
5 rooms
(iii)
R rooms?

Example
The number B is the sum of two numbers x and y.
write down an expression for B.

Example
The cost of a pen is 9 pence.
What is the cost of
(i)
3 pens
(ii)
12 pens
(iii)
n pens?

Example
Alan is three years younger than his sister Fiona. If Fiona is y
years old write down an expression for Alan’s Age.
If Fiona’s mum is three times her age. Write down an expression
for her age.

Example
The sum of three numbers is S and two of the numbers are a
and b. What is the third number ?

Example
A pen and pencil together costs x pence, and a pen alone
costs y pence. Find the cost of three pencils.

Example
The cost of a school outing to the theatre is £ C for the hire of
the coach plus £5 per child for tickets
a)
Write down an expression for the cost of 20 children
b)
When n children attend the theatre the total cost is £ T
Write a formula for T in terms of C and n.

Example
A bag of sweets is handed around the class and each student takes
4 sweets from the bag.
a)
If there are C people in the class, how many sweets are taken from
the bag?
b)
If there are 5 sweets left in the bag, and there were S sweets in
the bag at the start, write down a formula connecting S and C.