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On Monday, Lou drives his ford escort with 28-inch tires, averaging x miles per hour. On Tuesday, Lou
switches the tires on his car to 32-inch tires yet drives to work at the same average speed as on Monday. What is the percent change from Monday to Tuesday in the average number of revolutions that Lou’s tires make per second?
  • a)
    Decrease by 14.3%
  • b)
    Decrease by 12.5%
  • c)
    Increase by 14.3%
  • d)
    Increase by 12.5%
  • e)
    cannot be determined with the given information
Correct answer is option 'B'. Can you explain this answer?
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Verified Answer
On Monday, Lou drives his ford escort with 28-inch tires, averaging x ...
The key to solving this question lies in understanding the mathematical relationship that exists between the speed (s), the circumference of the tires (c) and the number of revolutions the tires make per second (r).  It makes sense that if you keep the speed of the car the same but increase the size of the tires, the number of revolutions that the new tires make per second should go down.  What, however, is the exact relationship?
Sometimes the best way to come up with a formula expressing the relationship between different variables is to analyze the labels (or units) that are associated with those variables.  Let’s use the following units for the variables in this question (even though they are slightly different in the question):
      c: inches/revolution   
      s: inches/sec
      r: revolutions/sec
The labels suggest:  (rev/sec) x (inches/rev) = (inches/sec), which means that rc = s. 
When the speed is held constant, as it is in this question, the relationship rc = s becomes rc = k.  r and c are inversely proportional to one another.  When two variables are inversely proportional, it means that whatever factor you multiply one of the variables by, the other one changes by the inverse of that factor.  For example if you keep the speed constant and you double the circumference of the tires, the rev/sec will be halved.  In this way the product of c and r is kept constant.    
In this question the circumferences of the tires are given in inches, the speed in miles per hour, and the rotational speed in revolutions per second.  However, the discrepancies here don’t affect the fundamental mathematical relationship of inverse proportionality: if the speed is kept constant, the rev/sec of the tires will change in an inverse manner to the circumference of the tires.    
Let’s assign     c1 = initial circumference; c2 = new circumference
r1 = initial rev/sec ; r2 = new rev/sec
Since the speeds are held constant:
c1r1 = c2r2
r2 = (c1/c2)r1
r2 = (28/32)r1  
r2 = (7/8)r1
If the new rev/sec is 7/8 of the previous rev/sec, this represents a 1/8 or 12.5% decrease and the correct answer is (B).  Relationships of inverse proportionality are important in any word problem on the GMAT involving a formula in the form of xy = z and in which z is held constant. 
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Most Upvoted Answer
On Monday, Lou drives his ford escort with 28-inch tires, averaging x ...
To solve this problem, we need to consider the relationship between the distance traveled and the number of revolutions.

The distance traveled is directly proportional to the number of revolutions. This means that if the distance traveled remains the same, the number of revolutions will also remain the same.

Since Lou drives to work at the same average speed on both Monday and Tuesday, the distance traveled will remain the same. Therefore, the number of revolutions will also remain the same.

This means that there is no percent change from Monday to Tuesday in the average number of revolutions. It remains constant at 100%.
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On Monday, Lou drives his ford escort with 28-inch tires, averaging x miles per hour. On Tuesday, Louswitches the tires on his car to 32-inch tires yet drives to work at the same average speed as on Monday. What is the percent change from Monday to Tuesday in the average number of revolutions that Lou’s tires make per second?a)Decrease by 14.3%b)Decrease by 12.5%c)Increase by 14.3%d)Increase by 12.5%e)cannot be determined with the given informationCorrect answer is option 'B'. Can you explain this answer?
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On Monday, Lou drives his ford escort with 28-inch tires, averaging x miles per hour. On Tuesday, Louswitches the tires on his car to 32-inch tires yet drives to work at the same average speed as on Monday. What is the percent change from Monday to Tuesday in the average number of revolutions that Lou’s tires make per second?a)Decrease by 14.3%b)Decrease by 12.5%c)Increase by 14.3%d)Increase by 12.5%e)cannot be determined with the given informationCorrect answer is option 'B'. Can you explain this answer? for GMAT 2024 is part of GMAT preparation. The Question and answers have been prepared according to the GMAT exam syllabus. Information about On Monday, Lou drives his ford escort with 28-inch tires, averaging x miles per hour. On Tuesday, Louswitches the tires on his car to 32-inch tires yet drives to work at the same average speed as on Monday. What is the percent change from Monday to Tuesday in the average number of revolutions that Lou’s tires make per second?a)Decrease by 14.3%b)Decrease by 12.5%c)Increase by 14.3%d)Increase by 12.5%e)cannot be determined with the given informationCorrect answer is option 'B'. Can you explain this answer? covers all topics & solutions for GMAT 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for On Monday, Lou drives his ford escort with 28-inch tires, averaging x miles per hour. On Tuesday, Louswitches the tires on his car to 32-inch tires yet drives to work at the same average speed as on Monday. What is the percent change from Monday to Tuesday in the average number of revolutions that Lou’s tires make per second?a)Decrease by 14.3%b)Decrease by 12.5%c)Increase by 14.3%d)Increase by 12.5%e)cannot be determined with the given informationCorrect answer is option 'B'. Can you explain this answer?.
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