Definition of invasive species ?

Invasive species are foreign species that are introduced to a new habitat and cause changes to the habitat.

Explanation:

Example is when the wolves were introduced to the yellowstonenational park again

in order to calculate the average, add the numbers and divide by how many numbers there are.  For example, if I want to know my test score average in a class and my test scores are 85, 90, and 70.  First add 85+90+70 = 245.  After that, divide by 3 because there are three test scores.  245/3 = 81.66.  The average test score is 81.66%