Word Problem that asks to give the monthly cost as a function of x

Question

A cell phone plan has a basic charge of $35 a month.The plan includes 400 free minutes and charges 10 cents for each additional minute of usage. Write the monthly cost C as a function of the number x of minutes used and graph C as a function of x for 0≤x≤600

Answer 1

C(x)= 35 if x≤400

C(x)= 35+0.10*(x-400) if x>400

 

The first one is in case you don't exceed the 400 min (It's valid when the number of minutes is lower or equal to 400). In that case, you will be paying always $35. The second one is in case you do exceed 400 min in that case you will be paying the basic charge of $35 plus $0.10 per each minute exceeding the 400 min.

Answer 2

C(x)=35 if x≤400

 

C(x)=35+0.1(x-400) if x>400