On a certain Monday, Carlos drove to work at an average

Question

Source: Veritas Prep On a certain Monday, Carlos drove to work at an average speed of 50 miles per hour and home from work along exactly the same route at an average speed of 70 miles per hour. Which of the following is closest to his average speed for both trips combined? A. 58.3 miles per hour B. 60.0 miles per hour C. 62.6 miles per hour D. 65.4 miles per hour E. It cannot be determined from the information given The OA is A

Brent@GMATPrepNow · Answer

BTGmoderatorLU wrote:Source: Veritas Prep On a certain Monday, Carlos drove to work at an average speed of 50 miles per hour and home from work along exactly the same route at an average speed of 70 miles per hour. Which of the following is closest to his average speed for both trips combined? A. 58.3 miles per hour B. 60.0 miles per hour C. 62.6 miles per hour D. 65.4 miles per hour E. It cannot be determined from the information given The OA is A Average speed = (TOTAL distance)/TOTAL travel time) Let d = the distance from work to home Carlos drove to work at an average speed of 50 miles per hour Time = distance/speed So, travel time TO work = d/50 hours Carlos drove home from work at an average speed of 70 miles per hour So, travel time FROM work = d/70 hours So, TOTAL travel time = d/50 + d/70 = 7d/350 + 5d/350 [rewrite with common denominators] = 12d/350 Also, TOTAL distance = d + d = 2d Which of the following is closest to his average speed for both trips combined? Average speed = (TOTAL distance)/TOTAL travel time) = (2d)/(12d/350) = (2d)(350/12d) = 700d/12d = 700/12 = 350/6 STOP. Since 360/60 = 60, we know that 350/6 will be LESS THAN 60 Answer: A Cheers, Brent

GMATGuruNY · Answer

BTGmoderatorLU wrote:Source: Veritas Prep On a certain Monday, Carlos drove to work at an average speed of 50 miles per hour and home from work along exactly the same route at an average speed of 70 miles per hour. Which of the following is closest to his average speed for both trips combined? A. 58.3 miles per hour B. 60.0 miles per hour C. 62.6 miles per hour D. 65.4 miles per hour E. It cannot be determined from the information given When the SAME DISTANCE is traveled at two different speeds, the average speed for the entire trip will be CLOSER TO THE LOWER SPEED than to the higher speed. The reason: The portion traveled at the lower speed takes LONGER. Since more time is spent at the lower speed than at the higher speed, the average speed for the entire trip will be closer to the lower speed. Here, halfway between the two speeds = the average of the two speeds = (50+70)/2 = 60. To be closer to the lower speed and to the higher speed, the average speed for the entire trip must be LESS THAN 60. The correct answer is A.

swerve · Answer

For these type of questions we can apply direct formula given below: 2ab/(a+b), where a & b are avg. speed. So 2x50x70/(120)= 58.33 (approx).

Scott@TargetTestPrep · Answer

BTGmoderatorLU wrote:Source: Veritas Prep On a certain Monday, Carlos drove to work at an average speed of 50 miles per hour and home from work along exactly the same route at an average speed of 70 miles per hour. Which of the following is closest to his average speed for both trips combined? A. 58.3 miles per hour B. 60.0 miles per hour C. 62.6 miles per hour D. 65.4 miles per hour E. It cannot be determined from the information given We can use the following formula: average rate = total distance/total time If we let the distance each way = d, then the time to work = d/50, and the time from work = d/70. Thus: average rate = 2d/(d/50 + d/70) average rate = 2d/(7d/350 + 5d/350) average rate = 2d/(12d/350) average rate = (2d x 350)/12d average rate = 350/6 = 58.3 mph Answer: A

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