Question

Jane has a pre-paid cell phone with Splint. She can't remember the exact costs, but her plan has a monthly fee and a charge for each minute of calling time. In June she used 260 minutes and the cost was $49.00. In July she used 940 minutes and the cost was $117.00.

A) Express the monthly cost C as a function of x, the number of minutes of calling time she used.

B) If Jane used 504 minutes of calling time in August, how much was her bill?

Answer 1

@DanJS

Answer 2

@sshayer

Answer 3

The total cost is a linear equation, and they give you 2 points of data. You can make a line equation.

Answer 4

Total Cost = Fee + Minute Charge * #minutes

The two points given are,
(x , C) = (260 , 49.00)
(x1 , C1) = (940, 117.00)

Remember the point slope line equation
y - y1 = m*(x - x1)
C - C1 = m*(x - x1)

Use the two points for that

Answer 5

x+260y=49
x+910y=117
find x and y

Answer 6

I tried that and it was wrong
ill try again

Answer 7

not 910 but 940

Answer 8

y=1/10x+23

Answer 9

is that correct?

Answer 10

@sshayer @DanJS

Answer 11

correct.

Answer 12

can you help me with part b

Answer 13

use x=504

Answer 14

so i do y-49=1/10(x-504)

Answer 15

\[C=\frac{ 1 }{ 10 }\times 504+23=?\]

Answer 16

omg im so off haha let me do that

Answer 17

527/10

Answer 18

50.40+23.00=

Answer 19

73.4

Answer 20

correct

Answer 21

sp thats the answer?

Answer 22

can you explain what you did there please? i have a test tomorrow and i dont quite understand 100%

Answer 23

in your equation x is the number of minutes

Answer 24

(x , C) = (260 , 49.00)
(x1 , C1) = (940, 117.00)

Those two points give a slope m=1/10

Using that slope m=1/10 and the point (260 , 49.00)

C - 49 = (1/10)*(x - 260)
C - 49 = (1/10)*x - 26
C = (1/10)*x + 23

The function is
C(x) = (1/10)*x + 23

Answer 25

I get that part, i dont get the second part

Answer 26

For x is 504 minutes...

C(504) = (1/10)*(504) + 23
= 367/5
= 73.40 dollars

Answer 27

ohh okayy! thank you so much!!