Q:

A car's speedometer has a percent error of 5%. The speedometer currently shows that the car is traveling at a speed of 60 mph.Which statement describes what the actual speed of the car could be?A.The actual speed of the car is either 30 mph or 90 mph.B. The actual speed of the car is either 55 mph or 65 mph.C.The actual speed of the car is either 57 mph or 63 mph.D.The actual speed of the car is either 58 mph or 62 mph.

Accepted Solution

A:
C.The actual speed of the car is either 57 mph or 63 mph.

Technically, none of the choices are correct since the percentage error is based upon the TRUE speed and not the erroneous reading. But given that this is just high school, I doubt your teacher took that into consideration and instead is providing the obvious choices. So first calculate 5% of 60,
0.05 * 60 = 3.

Now the lower limit will be 60 - 3 = 57 and the upper limit will be 60 + 3 = 63.
So the answer is "C"

As for my earlier comment the true lower speed assuming the speedometer was reading 5% high would be 57.14286 mph. 5% of that is 2.857143 and the sum is 60. And the higher limit would be 63.15789 mph and if the speedometer is reading 5% low, then 5% of the higher speed is 3.157895 and doing the subtraction will give you 60 mph.