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Do the Calculations – How to Create Equations

Math is one of the greatest parts of life.  The steps below will help you create equations for everyday life.

1. Identify the Constants

In our equation a constant is any number that does not change.  Since there are few things that remain totally constant in this world we have the flexibility to choose what is a constant.  An example might be the price of an item.  We can choose to have the price as a constant even though we know it will change over time but for the term that our equation is useful for it could be considered a constant.

2. Identify the Variables

Variables are numbers that change with time.  These numbers can be either predicable or unpredictable.  Examples would be the number of products you purchase at a store.  The number of months that you pay for Netflix.  While this is not an exhaustive list hopefully it gives you an idea on what we are looking for.

3. Identify the Relationships

Identifying the relationships between the numbers is when you figure out how the numbers should interact with each other.  Examples would be if you have the cost of a can of beans and you want to buy twelve cans.  You would multiply the two numbers to get the correct cost of beans for the twelve cans.  Another example would be if you bought an apple and an orange.  The cost of each would be added together which is their relationship to the final result.

4. Create the Equation

Now that we have the constants, variables and relationships we need to develop the order of operations.  This is where we identify what constants and variables need to be calculated first.


We are going shopping and we only have $10.  We have two items we want to buy, apples and bananas.  In this example we are going to assume there is no tax on the food.  This will make our calculations easier.  In later posts I will show you how to deal with taxes in your equations.  After going to the store we find that apple are $0.50 and bananas are $0.20.  Our grocery list says we need 12 apples for a pie we are going to make.  The rest of the money is for as many bananas as we can buy.

Constants: $0.50 per apple, $0.25 per banana, 12 apples for our pies, and $10 dollars

Variables: number of bananas we can buy

Relationships: Cost of apples is multiplied by number of apples, cost of bananas is multiplied by number of bananas, and by adding the total cost of the apples and bananas we get our total which should equal or be less than our $10.

Equation:  (Cost per Apple * Number of Apples) + (Cost per Banana * Number of Bananas) = Total Cost

Fill in the numbers: ($0.50 * 12) + ($0.20 * Number of Bananas) = $10

Single out our variable: Anything that can be calculated to get a single number should be done at this time.  In this equation we can multiply the apple portion of our equation to get a single number which will make our calculation easier.

New Equation: $6 + ($0.20 * Number of Bananas) = $10

Now we subtract the $6 from the $10 by moving it to the other side of the equals sign.  Then we divide by the $0.20 to get our number of bananas.

Answer: Number of Bananas = 20

Can you see an easier way to do the calculation?  We should be able to easily calculate the total cost of the apples in our head.  Once we have this number we know that we have $4 dollars left.  We also know from a simple calculation that at $0.20 a banana we can get 5 bananas for a single dollar.  We then take the 5 * 4 to get the total number of bananas we can purchase.

We used easy number in this example for ease of calculating.  Since more often than not you do not have to be exact in the real world you can use a rounding technique to help you calculate things quicker in your head.  An example would be if the bananas had been $0.22 per banana.  We could round this up to $0.25 to make our calculations easier.  Rounding to the nearest five or ten could have a huge impact if buying large amounts but with small amounts the error is low enough we can generalize those numbers.

I hope you find this useful.  When you create a simple set of rules to follow doing the calculations can be quite easy and very helpful in everyday life.

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