# Math Help: Useful Formulas to Remember

10/09/2015

## Math Formulas to Memorize

Here are a few math formulas that will come in handy in your math studies.

### Percentage and Percentage Change

To calculate the percentage, divide the part by the whole and multiply by 100: (Part/Whole)*100. For the percentage change, divide the difference by the original and multiply by 100: (Difference/Original)*100.

### Find Probability

The probability (P) of an event occurring is measured as a fraction (between 0 and 1) with 1 being 100% probability and 0 being 0%. Take the number of desired outcomes and divide by the number of possible outcomes. For example, if you want to know the probability of rolling a 3 on a six-sided di, it is 1 (because there is only one 3) over 6 (because there are 6 possibilities). To find the probability two, mutually exclusive events both occurring, multiply their probabilities. If you want to know the probability of rolling a 3 and then a 4, you would multiply 1/6*1/6 for 1/36.

### Average Speed

To find the average speed, use the formula distance over time.

### Quadratic Formula

Solve any quadratic equation in the form ax^2+bx+c=0 with this formula. For those formulas that are difficult to find the difference of squares, or if you are in a rush on an exam, the quadratic formula will be very nice to know.

### Quadratic Entities

You should know the three most common quadratic factors:

### Logarithms

You should understand logarithms and how to rewrite them.   asks b to what power (y) will result in x. You can rewrite it as:. When x is a product of two different numbers, it may be easier to solve if you remember the following formula:

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