# Solve for Unknowns in Scientific Equations

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• 0:01 Determining a Missing Value
• 0:44 Simple Algebra
• 3:51 Lesson Summary

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Lesson Transcript
Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

Calculating a missing value in an equation is something you may come across in your scientific analyses. As long as you know the relationship between the variables in the equation, as well as the rest of the measured values, this is a relatively straightforward process for you to master.

## Determining a Missing Value

As a scientist, a very useful skill to have is to be able to determine unknown values from known ones. In fact, this happens quite frequently as you work through data collection and analysis. For example, you may wish to know the density of an object, but you only know its mass and its volume. Or, maybe you want to know how fast something is travelling (its speed), but only know the distance that object travelled and the time it took to do so.

What's great is that as long as you know the other values, you can easily calculate the missing one by using simple mathematic relationships. Sometimes you may need to reorganize your formulas to get the known values together. But after you've done this, you're free to calculate away!

## Simple Algebra

Let's take a look at some examples of how we go about determining a missing value in an equation, which is any value in the equation that has not been measured or collected by other means. First and foremost, you have to know the formula! You may need to simply memorize some of the more basic ones, while others you can often look up online or in texts.

Next, you need to get all of the known values on the same side of the equation. For example, if you have the equation 2 + x = 5, you would subtract 2 from each side to get the unknown value, the x, by itself. You end up with 5 - 2 = x, and when you solve this you get x = 3. Pretty easy, right?

Let's try something a little more relevant. Let's say you have a chunk of copper and you know its density is 8.96 g/cm^3. You also know that the mass of the copper chunk is 25 g. It's not going to be easy to get the volume of your copper piece because there are no 'clean' straight edges to measure along. You could go find a beaker, fill it with water, dunk in the copper chunk, and then measure the volume of water that's displaced. This will certainly get you the volume of your mineral.

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