Question 159670
An overseas phone call is charged at one rate (a fixed amount) for the first minute and at a different rate for each additional minute. If a 7 min call costs $10, and a 4 min call costs $6.40, find each rate.
.
Let F = fixed rate
and R = additional minutes rate
.
Because we have two unknowns, we'll need two equations.  
Our first equation comes from "a 7 min call costs $10"
F + 7R = 10
.
Our second equation comes from "a 4 min call costs $6.40"
F + 4R = 6.40
.
Subtracting equation 2 from equation 2:
 F + 7R = 10
-F - 4R = -6.40
----------------
     3R = 3.60
R = $1.20 
.
To find F, substitute the above into equation 1 and solve:
F + 7R = 10
F + 7(1.20) = 10
F + 8.4 = 10
F = $1.60
.
Therefore:
Fixed rate is $1.60
Per minute charge after the first min is $1.20