Bunuel wrote:
The Kiljaro Highway is marked with Milestones denoting the distance to the town of Kiljaro. Tommy left kiljaro and drove the highway, passing the 10 km milestone at 8:30. Some time afterwards, Tommy got a phone call asking him to return home, and he made a U-turn at the 160 km milestone. At 09:A0 Tommy passed the milestone marking 70 km to Kiljaro. The variable A represents the tens digit of the minutes in 09:A0. Assuming Tommy maintained the same constant speed during the entire drive, how many kilometers did Tommy travel in one minute?
A. \(\frac{240}{30+10A}\)
B. \(\frac{240}{30+60A}\)
C. \(\frac{240}{40A}\)
D. \(\frac{220}{30+10A}\)
E. \(\frac{220}{40A}\)
Are You Up For the Challenge: 700 Level QuestionsWe can let A = 3. So in 1 hour, or 60 minutes, Tommy has driven (160 - 10) + (160 - 70) = 150 + 90 = 240 km. Therefore, his speed is 240/60 = 4 km per minute. Now let’s see which answer choice yields 4 when we substitute 3 for A.
A. 240/(30 + 10(3)) = 240/60 = 4 → Yes!
Even though we have found our answer, let’s prove it can’t the other choices. We don’t have to check choices B and D since they can’t be 4 (notice that B has the same numerator as A but a different denominator, whereas D has the same denominator as A but a different numerator).
C. 240/(40(3)) = 240/120 = 2 → No
E. 220/(40(3)) = 220/120 = 11/6 → No
Answer: A
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