Bunuel wrote:

Tim and Élan are 90 miles away from one another. They are starting to move towards each other simultaneously, Tim at a speed of 10 Mph and Élan at a speed of 5 Mph. If every hour they double their speeds, what is the distance that Tim will pass until he meets Élan?

(A) 30 miles.

(B) 35 miles.

(C) 45 miles.

(D) 60 miles.

(E) 65 miles.

In 1st hour: Relative speed of the two will be 10+5 = 15 miles / hour. As they move towards each other, The distance between them reduces by 15 miles. Distance left between them: 90 - 15 = 75 miles.

In 2nd hour: Speed of Tim: 20Mph, That of Elan: 10 Mph. Relative speed of the two will be 20+ 10 = 30 miles / hour. As they move towards each other, The distance between them reduces by 30 miles. Distance left between them: 75 - 30 = 45 miles.

In 3rd hour: Speed of Tim: 40 Mph, That of Elan: 20 Mph. Relative speed of the two will be 40+ 20 = 60 miles / hour.

Now in order to cover the remaining distance of 45 miles. They will take: (45/ 60) hrs. = (3/4) hour.

Distance travelled by Tim?

In first hour: 1 hour * (10 miles per hour) = 10 miles

In second hour: 1 hour * (20 miles per hour) = 20 miles

In third hour: (3/4) hour * (40 miles per hour) = 30 miles

Total distance travelled: 10+20+30 = 60 miles.

D is the answer.