thinking skills question tsa oxfordWatch
The train stops once en route: for 1 minute at Arwetheryet, 5 km from Offwego.
In both directions the train travels at an average speed of only 30 km/h between Offwego and
Arwetheryet because of a series of bends, but travels at a steady speed of 90km/h along the
straight track between Arwetheryet and Ellsware.
Trains depart from Offwego and Ellsware every hour at exactly the same time.
How long after departure do the two trains pass each other?
A 11½ minutes
B 12 minutes
C 12½ minutes
D 13 minutes
how is the answer c?
30 km/h = 0.5 km/min
And 90 km/h = 1.5 km/min
Also, the train from Ellsware is A, and the train from Offwego is B.
The stations look like:
O A E
It is 5km from O to A, and 21km from E to A.
Working backwards: train A is travelling at 1.5km/min * 12.5 min = 18.75 km travelled. Train A is now 18.75 km from E, or 7.25 km from O. (It hasn't reached station A).
It takes train B 10 minutes to reach station A. This is calculated by 5km / 0.5km/min. It then pauses for 1 minute. Now, it atarts travelling at 1.5km/min. 12.5 min - 10 min - 1 min= 1.5 min
1.5 min * 1.5 km/min = 2.25 km
5 km + 2.25 km = 7.25 km from O. This is the same as train A, so they are at the same place, so they pass each other at 12.5 min.
Maybe you forgot to include the pause? Sorry for the general untidiness!