A short presentation designed for use with the Construction Numeracy Unit at City of Glasgow College

1. Construction Numeracy
Using Percentages in the Construction Industry
Stonemasonry Department 2012

2. What is a Percentage?
A percentage is a value used to express a number as a fraction
of 100. A percentage is indicated by the symbol %. Can you
think of where you see or use percentages on a daily basis?
20%
DISCOUNT

3. Value Added Tax (VAT)
Value Added Tax (VAT) is a tax levied on products sold or
manufactured within the UK. It is currently set at 20% which
means that for every £100 you spend, £20 is claimed by the
Government.
Value x 1.2 = Value including VAT
for example
£100 x 1.2 = £120
There are a number of different ways to calculate VAT but the
easiest way is to establish the value of the items being bought
and multiply them by 1.2. This is because 1.2 is 120% expressed
as a decimal.

4. Value Added Tax (VAT)
Can you calculate how much VAT @ 20% would be applied to
the following amounts?
£75.00 =£90.00
£53.00 =£63.60
£28.60 =£34.32
£94.22 =£113.04
£135.00 =£162.00
How many did you get correct? You should find that regardless
of the amount, multiplying by 1.2 gives the value including VAT.
The original values are known as the value excluding VAT.

5. Calculating Discounts
Percentages are also commonly used to indicate discounts on
products and materials. For example you might be told that bags of
sand have 20% off normal retail price. This means that instead of
paying 100% of the normal value for the sand you pay 80%.
Without discount = £5.00
To apply the discount we multiply by 0.8 because 0.8 is
the way to express 80% as a decimal.
5.00 x 0.8 = 4.00
With discount = £4.00

6. Calculating Discounts
Can you apply discounts to the items shown below?
ALL
MIXERS 10% OFF
DOORS
15% OFF OVERALLS
25% OFF
RRP* £120.00 £315.00 £18.00
Discounted £90.00 £267.75 £16.20

7. Calculating Wastage
If you order the exact amount of materials for a job it is likely
you wont have enough due to wastage and breakages. To avoid
this we order additional materials, usually shown as a
percentage.
+10%
1000 blocks 1100 blocks
In the example shown above there are 1000 mono-blocks
required for a project. An additional 10% of required mono-
blocks are ordered to allow for wastage and breakages.
1000 bricks x 1.1 = 1100 bricks

8. References
The image on the second slide of this presentation was
sourced from http://www.diabetic-dieting.com/food-
label_files/Visual-Food-Label.jpg
This image was made available under creative commons
The image on the second slide of this presentation was
sourced from http://psdhunter.com/psds/3633-progress-
bar-by-milos-milikic.png
This image was made available under creative commons

9. Developed by The Stonemasonry Department
City of Glasgow College
2012