An intelligent trader carries 3 sacks having 30 coconuts each. On the way he passes through 30 checkpoints. On every checkpoint he has to give one coconut each from each sack. How many coconuts does he have left?

Note: Initially,  it will look you quite simple and you think it is zero.

But here you have to emphasise on the word An intelligent trader, so you need to think according to an intelligent trader.

Being an intelligent trader he will definitely use all his intelligence to get the profit that is by trying to safe as much coconut as possible so

3 sacks each having 30 coconut total= 90 coconuts.

Now 30 check point and at each checkpoint he has to give coconut as much he have number of sack so, for the first 10 checkpoint he will use only one sack and give 30 coconuts.

Now he left with 2 sacks and 20 check points.

So for next 15 checkpoint he will use another sack and give coconuts from it.

After this he is left with 1 sack and 5 check points so by giving one at each point he will left with 25 coconuts.

So finally 25 coconut is left.