Percentages

1
Percentages
Objectives B Grade Understand how to calculate
successive percentages Work out compound
interest
Prior knowledge
Understand
Finding percentages of quantities calculator
and non calculator
Percentage increase / decrease percentage
multipliers
2
Percentages
Successive increase or decrease questions will
have a percentage increase / decrease that is
repeated more than once.
Example
1000 is put in a bank account that pays 5
interest at the end of each year. Calculate how
much there will be after 3 years.
Answer
At the end of the first year there will have been
a 5 increase
The percentage multiplier for a 5 increase is
1.05
Original quantity percentage multiplier new
quantity
1000 1.05
1050
At the end of the second year there will have
been a 5 increase
1050 1.05
1102.5
At the end of the third year there will have been
a 5 increase
1157.625
1102.5 1.05
1157.63
3
Percentages
Look at what has been done here
1157.625
( ) 1.05
( ) 1.05
1000 1.05
This can be simplified to
1000 1.053
The index number represents the number of times
the percentage change is repeated
Look at the difference by calculating one years
percentage increase Then multiplying it by 3
5 of 1000
1000 0.05 50
50 3 150
1000 150
1150
This is called simple interest because it does
not calculate 5 of the new quantity at the end
of the first year