A long distance calling plan charges 89 cents

[wiishesssss]

A long distance calling plan charges 89 cents for any call up to 15 minutes in length and 6 cents for each additional minute or part of a minute.
a. Write a formula for the cost C, in terms of the length of a call t, in minutes.
b. State the domain of the function in part a.
c. On graph paper, sketch the function using an appropriate scale.

This is what i got:
a) Cost = c =
c = f(t)
c = 89, 0 < x < or equal to 15
6x, x > 15

b) Domain of the function in part a.
Domain for 89: [0, 15)
Domain for 6x: (-00,00)
Domain: [0,00)


is that correct?

 

[skeeter]

A long distance calling plan charges 89 cents for any call up to 15 minutes in length and 6 cents for each additional minute or part of a minute.
a. Write a formula for the cost C, in terms of the length of a call t, in minutes.
b. State the domain of the function in part a.
c. On graph paper, sketch the function using an appropriate scale.

This is what i got:
a) Cost = c =
c = f(t)
c = 89, 0 < x < or equal to 15 ok ... I'd use t for time instead of x
6x, x > 15 c = 89 + 6(t-15), t > 15

b) Domain of the function in part a.
Domain for 89: [0, 15) (0, 15]
Domain for 6x: (-00,00) (15, inf)
Domain: [0,00) how can you talk for "0" minutes?


is that correct?

 

[wiishesssss]

thank you .. another quick question would you put 89 or .89 because we are talking in cents?

and then if we did use .89
c = .89, 0 < t < or equal to 15
then c = 89 + 6(t-15), t > 15 would change to
c = .89 + 0.06(t-15), t > 15

 

[Mrspi]

thank you .. another quick question would you put 89 or .89 because we are talking in cents?

and then if we did use .89
c = .89, 0 < t < or equal to 15
then c = 89 + 6(t-15), t > 15 would change to
c = .89 + 0.06(t-15), t > 15

If "we're talking in cents" it would be 89......


And answers you get for substituting different values for t (the number of minutes) would also be in cents...

Your second equation is correct if you want the cost in dollars and cents.

 

[Denis]

> ...and 6 cents for each additional minute "or part of a minute."

.89 +.06|t - 15 +.99| ?