Math

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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.

  • Math -

    Variables,
    X=first, (fixed) rate
    y=second, rate(/minute)
    t=time of call
    z=total cost
    Equation,
    z=x+((t-1)*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+((7-1)*y), 6.4=x+((4-1)*y)
    10=x+(6*y), 6.4=x+(3*y)
    10=x+(6*y), 6.4=x+(3*y)
    -6y= -6y, -3y= -3y
    10-6y=x, 6.4-3y=x
    10-6y= 6.4-3y
    -6.4=-6.4
    3.6-6y=-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
    10-6y=x
    10-6(1.2)=x
    10-7.2=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.

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