Question

A cell phone plan charges $45.75 per month, plus $9.55 in taxes, plus $0.35 per

minute for calls beyond the 500-min monthly limit. Write a piecewise defined
function to model the monthly cost C(x) as a function of the number of minutes used
x for the month.

Answer 1

Answer: We can write the piecewise defined function for the monthly cost C(x) as follows:

C(x) =

45.75 - 9.55, if x ≤ 500

45.75 - 9.55 + 0.35(x - 500), if x > 500

Step-by-step explanation:

For the first 500 minutes, the monthly cost is a flat rate of $45.75 for the plan fee and $9.55 for taxes, so the total cost is simply the sum of these two amounts: C(x) = 45.75 + 9.55 = 55.30, for x ≤ 500.

For any additional minutes beyond the 500-min limit, there is an additional charge of $0.35 per minute, so the cost increases linearly with the number of extra minutes used. The expression (x - 500) represents the number of minutes beyond the limit, so we multiply this by the rate of $0.35 per minute and add this amount to the base cost of $55.30, giving the piecewise expression:

C(x) =

55.30, if x ≤ 500

55.30 + 0.35(x - 500), if x > 500

Therefore, the piecewise defined function for the monthly cost C(x) is:

C(x) =

45.75 - 9.55, if x ≤ 500

45.75 - 9.55 + 0.35(x - 500), if x > 500

Note: The two expressions are equivalent, but the second expression is simplified by combining the constants.

Step-by-step explanation: