Question

A mobile company charges a fixed rate of x cents per minute for the first 120 minutes of talk time and another rate of y cents per minute for each additional minute of talk time. Ethan paid $26.80 and $32.40 for 175 mins and 210 minutes of talk time on two different occasions respectively. find the amount he has to pay if he uses 140 mins of talk time.

Answer 1

Answer:

$21.2

Step-by-step explanation:

From the problem given, we express them as algebra so that we can easily solve;

    the total charge on a call greater than 120min is given as;

   120x + y(n - 120) = total cost of call

where n is the number of minutes which is greater than 120;

•   Ethan paid $26.80  for 175 mins

  n = 175min here;

      120x + y(175 - 120) = 26.80

       120x + 55y = 26.80 ----- (I)

• $32.40 for 210 minutes

      n = 210min

       120x + y(210 - 120) = 32.4

       120x + 90y = 32.4 ----- (II)

Now let us solve both equations for y and x;

      120x + 55y = 26.80 ----- (I)

     120x + 90y = 32.4 ----- (II)

subtract the two equations;

             90y - 55y = 32.4 - 26.8

                  35y = 5.6

                       y = $\frac{5.6}{35}$  = 0.16cents

then x;

       120x = 26.8 - 55y from equation I

       120x = 26.8 - 55(0.16)

       120x = 18

            x = $\frac{18}{120}$  = 0.15cents

Find the cost of 140min of talk time;

  n =140min;

      =  120(0.15) + 0.16(140 - 120)

      = 18 + 0.16(20)

      = 18 + 3.2

      = $21.2