Kristin wants to adopt a dog

Question

Kristin had initially planned to save money each week. The function, f(x)=55x+15 , modeled her money saved, f(x), after x weeks. Would it take Kristen longer to save the 400 according to this model, or to pay back the loan from her grandmother? Use mathematics to support your answer.

Answer 1

We can figure out how long it'll take to save $400.

400 = 55x + 15

55x = 400 - 15 = 385, so x =385/55 = 7 wks.

How compare that with loan from grandma?