Eric has been donating books he no longer needs to his local library. After 3 months of donating, he had 157 books left in his room. After 8 months of donating, he had 102 books left in his room. How many books per month did Eric donate on average between months 3 and 8?

a-31 books per month

b-18 books per month

c-11 books per month

d-7 books per month

Question

Eric has been donating books he no longer needs to his local library. After 3 months of donating, he had 157 books left in his room. After 8 months of donating, he had 102 books left in his room. How many books per month did Eric donate on average between months 3 and 8?

a-31 books per month

 b-18 books per month

 c-11 books per month

 d-7 books per month

mathmale · Answer

This is a rate, or slope, problem.  Think of the given information as consisting of two points:  (3 months, 157 books) and (8 months, 102 books).

Find the slope of the line through these two points.