Math
posted by Jamese on .
A international phone call cost a fixed amount for the first minute and a certain rate per each additional minute. If a 7 minute phone call cost $10 and a $4 call cost &6.40, find the fixed charge and the rate per each additional minute.

Variables,
X=first, (fixed) rate
y=second, rate(/minute)
t=time of call
z=total cost
Equation,
z=x+((t1)*y)
Values,
7minutes is $10, 4minutes is $6.40
Plug them in, isolate one variable, set them equal to each other, and solve for the remaining variable,
10=x+((71)*y), 6.4=x+((41)*y)
10=x+(6*y), 6.4=x+(3*y)
10=x+(6*y), 6.4=x+(3*y)
6y= 6y, 3y= 3y
106y=x, 6.43y=x
106y= 6.43y
6.4=6.4
3.66y=3y
+6y=+6y
3.6=3y
(3.6)/3=(3y)/3
1.2=y
pick one original equation, plug in your new value, and solve for the remaining variable
106y=x
106(1.2)=x
107.2=x
2.8=x
Fixed first minute is $2.80, with $1.20 per each additional minute
I gave you the equations so that you could have them to help you on later problems. And I hope the directions helped.