Question

Pistacchio is training for the ironcat and has to run from our office in Mexico City to Puebla ROUND TRIP, at an average speed of 50 kms per hour.

The issue is that on the way out he stopped to change a tire on an old woman’s car, so her average speed was only 25 km per hour.

How fast do you have to return to be able to fulfill your mission that in the round trip your average speed is 50 km per hour?

Options:

1. At 75 kms per hour. It was 25 kms per hour less than what was due on the way out, you must compensate with 25 kms per hour more on the return.
2. At 100 kms per hour. He was at half speed in the first leg, must return at double speed in the return.
3. Pistacchio must teleport back. Thus he fulfills his mission and incidentally breaks some laws of physics, which is the only thing he needs to be my hero.
4. No idea, but I would like to understand how you could change the tire without having opposable thumbs.

Answer:

The only way for Pistacchio to accomplish his mission is to teleport back (3). In this problem, the distance between the cities of Mexico and Puebla is totally irrelevant. The only relevant thing is to think in terms of time. If Pistacchio has to go 50 kms per hour on average but went 25 kms per hour in the middle of the journey … he already used all the time he had available to complete the trip.

For example, let’s assume that Mexico City and Puebla are 100 km apart. If he had gone at 50 kms per hour, it would have taken him two hours to get to Puebla, and two hours to get back to Mexico (total 4 hours). But if the outward journey was at 25 kms per hour … the outward journey time would have already been 4 hours. No speed except snapshot would allow him to accomplish the mission.