# Tiffany has been dieting for 6 months. After 1 month Tiffany lost a total of 8 pounds. After 6 months, she lost a total of 25 pounds. How do you find the average rate of change of pounds per month?

##### 1 Answer

She **loses** 3.4 pounds per month.

#### Explanation:

We want to calculate Tiffany's average rate of change of weight over a time period. To do this, we'll be employing the following formula:

..where **amount of weight Tiffany has lost** at any given time.

We know that she'd lost 8 pounds after 1 month, and 25 after 6. Therefore, we have an initial weight loss, final weight loss, and a time interval. All we need to do, therefore, is plug it all in:

**lost** per month

Notice my vocabulary in that final answer: I make sure I specify that I'm saying that she's *lost* that much weight per month. It's important to make this distinction, since the answer 3.4 pounds per month can very easily be interpreted as a gain in weight, which is not what we're saying. So, make sure you're meticulous about that.

This video I made explains the concepts of average rates of change, and relates them to the study of derivatives, which you'll likely be doing soon:

Hope that helps :)