Counting Number of Items Beginning Before and Finishing After a Defined Number

Hi

I have this problem where I am trying to count the number of fish present in a video frame. I have each fish's entry frame no. and exit frame no. and I created a series of random numbers. I want to count the number of fish that are present at each random number. I think the COUNTIF function might be of some help? I have attached a simple worksheet with an example of the problem.

If I understand your sheet right, you have (5) fish total.

this formula tells how many fish were present in frame 26:

=SUMPRODUCT((--(A$2:A$6<=26))*(--(B$2:B$6>=26)))

thanks mate, works a charm!