Wealthy Maths: Calculating cost per use

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Cost per use is a useful way to compare various options before you make a purchasing decision. It allows you to evaluate the options and select the one that gives you the best bang for your buck.

Cost per use is defined as the number of rands you spend on every “use” of an item.

So, how do you calculate cost per use?

In maths, “per” means divide. So to get the cost per use, you take the total cost and divide it by the total use.

Total Cost

This is the total price you pay. Usually, it’s just the price on the sticker, but it can get more complicated if there are extras, like delivery fees etc.

Total Use

Ex: The total use of a coffee machine can be expressed as the total number of cups of coffee you’ll get from the machine. The total use of a television can be measured in the total hours of use that you’ll get from the television.

Calculating cost per use – a real-life example

I’m planning to enter the Comrades 2019 marathon and I’m going to need a new pair of running shoes.

A good measure of the “use” of running shoes is kilometres. Running shoes start losing its cushioning and protection as you use them, and should be replaced to avoid injury. A good rule of thumb is that running shoes should be replaced every 700km – 900km. So let’s use the middle of the range, 800km, in our calculation.

A pair of Speedy Shoes costs R2,200 and a pair of Quick Kicks R3,500. To calculate the cost per use, divide the total cost by the total use. In this case, the total use is 800km for both pairs.

Total Cost Total Use Cost per Use
Speedy Shoes R2,200 800km R2.75/km
Quick Kicks R3,500 800km R4.38/km

In this example, a pair of Speedy Shoes works out much cheaper per kilometre than the Quick Kicks. In fact, as long as it can do 800km, the cheaper pair will always come out tops because the total kilometres are the same.

But let’s say the Quick Kicks had some new, yet to be invented, technology that made the cushioning and protection last longer. They only need to be replaced after 1 500km.

Total Cost Total Use Cost per Use
Speedy Shoes R2,200 800km R2.75/km
Quick Kicks R3,500 1500km R2.33/km

In this case, the Quick Kicks comes out tops, offering better value for money.

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