Engr2012 wrote:
RSOHAL wrote:
John would have reduced the time it took him to drive from his home to a certain store by 1/3 if he had increased his average speed by 15 miles per hour. What was John's actual average speed, in miles per hour, when he drove from his home to the store?
(A) 25
(B) 30
(C) 40
(D) 45
(E) 50
Source: GMAT Focus
Let v,t be the original speed and time taken by John
As the total distance (=speed*time) must be the same,
v*t = (2t/3)*(v+15) ---> v=30 miles per hour.
B is the correct answer.
I like the way you approached the question.
I tried to solve the question in a similar way, but without success

the new time given is equal to x-1/3, while the distance is the same and the John's rate changed, which is equal to Disatnce/time - 1/3.
In this way I got this equation: x-1/3=D/T-1/3... after that I was stucked.
Where did I fail?