Homework Help: math

Posted by kathy m. on Sunday, December 30, 2012 at 9:46pm.

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 - kathy m., Sunday, December 30, 2012 at 9:47pm
i just really need help with c. i know a is $45 and b is 102 mph but i dont get c
math - Reiny, Sunday, December 30, 2012 at 11:25pm
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 - kathy m., Sunday, December 30, 2012 at 11:41pm
yeah, i found out b was wrong after working it out again, but thanks so much for explaining c~

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