Construction NumeracyCalculating Ratios and Proportions Stonemasonry Department 2012
Perimeter ‘a ratio represents, simply, for every amount of one thing, how much there is of another thing’ Wikipedia 2012
Ratios Ratios are used by all trades in the construction industry. One of the most common uses for ratios is when specifying a mortar mix. For example the image above shows that in order to mix the specified mortar 5 buckets of sand and 2 buckets of lime are used. This is known as a 5:2 mix.
Ratios Can you identify the ratio of sand to lime in the mortar mixes shown below? = 4:1 = 3:1 = 3:2 = 4:2
Ratios In the last example on the previous slide we established a ratio of 4:2. When using ratios we normally try to reduce them to their simplest form. This means that rather than saying 4:2 we divide each side by 2 and get a ratio of 2:1. : :
Ratios Which of the ratios shown below is the odd one out? That’s right the 5:2 is the odd one out as all the others are variables of 3:1.
Ratios It is not only mortar mixes that are shown as ratios. In the construction industry workers are often placed into small squads so that they are able to work efficiently. An example of this is the bricklayers 2 and 1 squad where one labourer is assigned to work with 2 bricklayers. :
Ratios In previous examples we simplified the ratios to make them more easy to understand. We can however also multiply ratios to calculate how many of one value we need in proportion to another value. Using a ratio of 2:1 can you calculate how many labourers are required to service 40 bricklayers? : x20
Ratios We can also have ratios which show the value of three or more different things. We have now added some colouring dye to our mortar mix from earlier. Can you guess how the ratio might be displayed? 5:2:1 The mix is now referred to as a 5:2:1 mix as there are five parts sand to two parts lime to one part colouring dye.
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