[SunilNagpal]

Ans would be 1440.

10+5+20+15=50

36000m/50m = 720.

Since we included both car n truck hence total no. 2x720= 1440

Thanks for approaching the question Ronit, atleast you put forward a point that one shouldn't just assume , but should rather try.....was this another question from GATE only?

Since it's an open discussion, I wished to add a point of view and also seek some clarification...

If I approach it in following way, let's see what comes out (haven't tried it, just writing the attempt extempore)...

1. Length of bridge (B) in metres
2. Number of cars that can cover the entire bridge © = B ÷ (Length of car + gap between cars)
3. Number of trucks that can cover the entire bridge (t)= B ÷ (Length of truck + gap between trucks)
4. Number of bridge lengths that can be covered per hour (N) = 36000/ B
5. Number of vehicles that can travel on the bridge in one hour = N× c + N×t or N(c + t)
= (36000/B)× B/[(1/20) + (1/30)]
= 36000/20 + 36000/30
= 1800 + 1200 = 3000

Now, the problem with this approach is that we are assuming that cars n trucks are individually driving through the bridge with no alternating.

So, if we alternate, then both trucks and cars will get only half of the chance of going through the bridge....

Making it 3000/2 = 1500 vehicles.....I might be completely wrong if that was not even an option, (as I was wrong in assuming that bridge length is important)...but definitely do let me know how the approach is flawed if 1500 is not even an option...

About alternating...
If it is c t c t c t c t then gaps won't make sense. So thought of sending cars in one go then trucks in the next turn..

N guys it's fun to be back on these tracks out of the routine corporate work..thanks for sharing the problem