A particular cell phone plan charges a monthly fee of 20 tha

A particular cell phone plan charges a monthly fee of $20 that includes up to 400 text message. For each text message above the included 400 but below texts, it charges $0.35 per text. For the 700 the message and above, it charges $0.30 per text. Find a a piecewise-defined function. T(x)_, that will allow a cell phone user to determine the total amount of their monthly text message bill if they use times text messages.

Solution

Monthly fee---$ 20 ---( 400 text messages)

Upto 400 text msgs i.e = 400 for 0< = x<= 400

For text messages above 400 but below 700 ----- $ 0.35 per text msg.

For text messages above 400 but below 700 = 0.35x ; 400<x < 700 ( where xis the no. of text msgs

For above and including 700th text msg, charges----- $ 0.3 per text

For above and including 700th text msg, charges = $ 0.3x ; x>= 700

So, function T(x) for text msg charges : = $ 20 for 0< = x<= 400

=  $ 0.35x for 400<x < 700

= $ 0.3x for x>= 700