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Suppose that a certain municipality uses the equation y=3(x-50)+30 to determine the fine assessed a car which exceeds the 50 mph speed limit. Let x=speed of the car (in mph) and y=corresponding fine in dollars.

a)What is the fine for traveling at 55 mph?

b)If the fine is $126, what is the speed of the car?

c)If car A travels at 60 mph and car B travels at 90 mph, then car B is traveling 50% faster than car A. However the fine for car B is what percent higher than that of car A?

  • math -

    i just really need help with c. i know a is $45 and b is 102 mph but i don't get c

  • math -

    I disagree with your b) answer of 102

    3(x-50) + 30 = 126
    3(x-50) = 96
    x-50 = 32
    x = 32+50 = 82 mph

    c) fine for A is 3(60-50) + 30 = $60
    fine for B is 3(90-50) + 30 = $150

    increase in speed = 30 mph
    increase in fine = 150-60 = $90

    percentage increase = 90/60 = 1.5 or 150% increase in the fine.

  • math -

    yeah, i found out b was wrong after working it out again, but thanks so much for explaining c~

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