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Mathematics>Standard Multiple Choice

Read the following SAT test question and then click on a button to select your answer.

The odometer of a new automobile functions improperly and registers only 2 miles for every 3 miles driven. If the odometer indicates 48 miles, how many miles has the automobile actually been driven?

(A) 144
(B) 72
(C) 64
(D) 32
(E) 24

答案和解析

答案：B

解析：

In this problem, you are told that the odometer registers only 2 miles for every 3 miles driven. So the ratio of miles registered to miles driven is 2 to 3 or 2/3. This can be expressed as

odometer reading/actual miles = 2/3

If the odometer indicates 48 miles, the actual miles can be found using using the above relationship as follows:

48/x = 2/3 and 2x = 144 and x=72

So if the odometer indicates 48 miles, the actual number of miles driven is 72.

How to Avoid Errors When Working with Ratios

The most important thing with ratios is to be consistent in the way you set them up. If you mix up the terms, you won’t get the correct answer. For instance, if you put the registered mileage in the numerator of one ratio but the actual mileage in the numerator of the other ratio, you will come up with a wrong answer: