Melody

Let there be k students in front of Reim.

So there is  k students in front + 3k students behind + Reim = 4k+1 students

Let N be the number of students in front of Bindu. 

So there is N students in front + 4N students behind + Bindu = 5N+1 students

4k+1=5N+1

4k=5N

So the number of students is a product of both 4 and 5 + 1 more

20 is the only such product that is less than or equal to 30

So there are 21 students in the line.

Bindu is 5th and Reim is 6th.

You can, you even should, so long as you are 'fair' about it.

You should be at least as generous to other people's answers as you are to your own.

And

You should only give yourself a point if your answer actually deserves it.

------------------

Some people make a habit of adding a string of mind-numbing posts and then give themselves multiple points for each post.

Often these same people never give any one else a point.  

This type of behaviour is not acceptable and it does not go unnoticed for long.

NOTE:

I am not accusing LuckyDuck of ever behaving in this way.  

Actually guests logic is simpler than mine and it is also correct.

Nicely done guest!

I agree with 6/23

I did it with a probability tree.

Say you chose a   red wood triangle

there are 2*3*4 = 24 blocks, you chose one and there are 23 blocks left

12 of those are NOT wood

Of the 12 that are not wood, 2/3 of them  are not red, that is 8 are not red or made of wood

Of these 8, 3/4 of them are not a triangle so that is 8*3/4 = 6 are not made of wood, or red or a triangle

So that is   6/23 will not share any of the same traits.

If you draw a probability tree it might be easier for you to see.

You didn't actually have to delete it. You only had to edit it and give proper credit to the person or site that it came from.   

Mind you, those questions and answers are copyrighted I think. 

I am not sure what that means exactly, I think you can give a link to it but you probably are not supposed to copy it over.

Thanks LuckyDucky   

Wouldn't it be the smallest positive integer N that you are looking for?

Plagiarism is a serious offense.

You must not ever take someone else's work and present it as your own.

You can give a link to a site if you wish. Or at the very least state clearly where your answers come from.

Did you copy your answer LuckyDuck?

Thanks Chris :)