The average (arithmetic mean) of 5,10,15 and x is 20..what is the x ? how do i solve this question?

How is working backward similar to solving an equation?

You are shooting hoops after school and make 152 out of a total of 200. what percent of shots did you make? what percent did you miss? show proportion(s).

Suppose you are an avid reader and are looking to save money on the cost of books instead of paying about $20 for each book, you decide to look into purchasing a kindle for $120 you can purchase e-books for about $5 each 1. find the slope-intercept equation for the cost of the hard copy of books using x to represent the number of books 2. find the slope-intercept equation for the cost of the kindle with cost of e-books using x to represent the number of books