2012-02-06 09:00:28

Carly ran a certain distance on Monday, then set a goal of increasing her distance each day of the week. For the next four days, she ran 10% farther than she ran the previous day. Approximately what percent of Monday’s distance did she run on Friday of that week?

(A) 110%

(B) 121%

(C) 136%

(D) 140%

(E) 146%



The correct answer is E.

Explanation: There are a couple ways of approaching this question, which focuses on percentages, a favorite topic of the test makers. You could use algebra, but it’s probably easier to use some strategic thinking.

The best thing to do in a question like this is to plug a number in for Carly’s starting distance.  Whenever you have a percentage question that does not give you a starting value, use 100, because it’s the easiest number to work with. Thus, let’s say she ran 100 miles on Monday (Carly could be a really great runner, right?); then, on Tuesday, she would have run 10% more than 100, or 110 miles (since 10% of 100 is 10). On Wednesday, she would have run another 10% of 110 miles, or 11 miles more for a total of 121 miles. On Thursday, she would have run another 10% of 121 miles, which is 12.1 miles, for a total of 133.1 miles. And on Friday, she would have run another 10% of 133.1 miles, which is 13.31 miles, for a total of 146.41 miles. The percent of Monday’s distance she ran on Friday would then be simply the quotient of Friday’s and Monday’s distances, or 146.41/100, which is 1.4641. As a percentage, this is 146.41%, which is approximately 146%. Thus, choice E is correct, and you found it without using that pesky algebra (side note: to solve it algebraically, use m for her starting distance and multiply it by 1.1 x 1.1 x 1.1 x 1.1 to account for her distance traveled each additional day… you’ll get the same answer).