How to use the inverse variation formula

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ACT Math › How to use the inverse variation formula

Questions 1 - 4
1

In a given set of experiments, the values of two variables are always inversely proportional. If in the first experiment the first variable was and the second was , what could you expect the second variable to be if the first is in a later experiment?

Explanation

Recall that inverse variation means that when one variable increases, the other decreases. This gives you the following equation:

Now, for our data, we know:

You merely have to solve for :

Divide by :

2

Throughout a party, the number of joyful non-philosophers in a room is always inversely proportional to the number of philosophers in the room. The room begins with people, of whom are philosophers. Later in the day, there are philosophers in the room. How many joyful non-philosophers are at the party at the later time?

Explanation

Recall that inverse variation means that when one variable increases, the other decreases. This gives you the following equation:

For our data, this means:

You merely need to solve for :

3

varies inversely with . When , . What does equal when ?

Explanation

1. Use the given values of and to solve for :

2. Solve for when in the above equation:

4

If , what is the value of ?

Explanation

To solve this algebraic equation, subtract from both sides, and then subtract from both sides.

We end up with the equation , for which the solution is:

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