A long distance telephone company advertised the rates of 5 minutes for 85¢ and 10 minutes for $1.10.

Use a linear equation to find the cost of a 25 minute phone call.

Question

A long distance telephone company advertised the rates of 5 minutes for 85¢ and 10 minutes for $1.10.

Use a linear equation to find the cost of a 25 minute phone call.

anonymous · Answer

find the equation of the line through the points (5,85) and (10,110)

anonymous · Answer

slope is 
$$\frac{110-85}{10-5}=\frac{25}{5}=5$$

anonymous · Answer

use point slope formula to get 
$$y-y_1=m(x-x_1)$$
$$y-110=5(x-10)$$
$$y-110=5x-50$$
$$y=5x+60$$

anonymous · Answer

interpretation is you get charged 5 cents a minute and 60 cents to connect the call. replace x by 25 to get 
$$y=5\times 25+60=125+60=185$$ or $1.85