# Algebra Substitution – Positive Numbers

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In Basketball we can have certain set positions on the court, and substitute player names into these positions.

This gives us one unique team who will play for us during the match.

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We could choose a different team with some different player names, and this would give us a different result.

Our Team Positions chart sets up where we can substitute our players, and we can pick several different names to substitute into this chart.

In Algebra, we have an “Expression” that tells us what different variable letters we have available to substitute numbers into.

The Algebra Expression is like our Basketball Positions Chart.

The Basketball Chart sets up Positions, that we can then substitute Names into.

The Algebra Expression sets up letter Variables, that we can then substitute Numbers into.

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Evaluating Expressions Video

Watch the following video which shows how we do basic Algebra Substitution.

Substitution Steps

As per the video, we follow a specific set of steps to work out a substitution question.

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Here is the full working out for the example question.

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We need to set out a question like this in our workbook as follows:

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Worked Examples

Here are some examples of typical Algebra Substitution questions.

The following working out shows a classic beginner mistake.

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Letters and Numbers joined to each other need to be multiplied together.

Here is the correct working out for this question.

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The next example shows how to do a two letters substitution.

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In the next example we have a three letter substitution question.

It is very important in these questions to remember to process the operations on the numbers in BODMAS / PEMDAS order.

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In “Example 3″ below, we do Multiplication and Division first, and the addition of the c = 4 value needs to be done last.

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In our next example we have multiplying brackets.

Because of BODMAS / PEMDAS required order, we do the inside of the brackets first, and then multiply by the outside bracket number last.

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Values Tables Substitution

We sometimes need to use a supplied rule equation to complete a values table of “x” and “y” values.

These tables are used when we need to draw a graph for the rule. However we will not be drawing the graph in this example.

If you want to see an example where we make the graph from the completed values table, then click the lesson link below:

http://passyworldofmathematics.com/plotting-graphs-from-t-tables/

This next example is basically four separate substitution questions, where we are putting our four answers into an answer table.

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We now need to work out “y” answers for the other three “x” values the same way.

At Passy’s World we find it easiest to do these questions by adding a middle column to the table where we do the working out.

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Algebra Substitution Videos

The following is a very short one problem video made by some math students.

This next video shows a couple of example questions that involve substitution.

Here is a video which gets into working out some challenging exponents questions.

That completes our lesson on evaluating algebra expressions using normal positive numbers.

In the next lesson, we look at substitution questions that use a mixture of positive and negative numbers.

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Passy