Question

The monthly cost for 45 minutes of calls is $13.31 and the monthly cost for 74 minutes is $16.50. What is the monthly cost for 58 minutes of calls?

Answer 1

The cost for 58 minutes is $14.74

Explanation:

Assuming that the graph of cost versus time varies linearly,

the given 2 coordinates are (45,13.31) and (74,16.50).

Let the cost for 58 minutes be "y".

The third coordinate is (58, y) , which lies on the line joining the above 2 points.

The slope of the line is

m =
`((16.50)-(13.31))/((74)-(45))`

m = 0.11

The equation of line is,

`(Y - 13.31) = m(X - 45)`

`(Y - 13.31) = (0.11)(X - 45)`

Inserting third point in above equation, we get,

`(Y - 13.31) = (0.11)(58- 45)`

`Y = 14.74`

Thus, the cost for 58 minutes is $14.74