Looking to find "interval"/"output" function

[Punssiliini]

Hello, I have a problem finding function to do the following. (I've forgot the mathematic term for this type of calculation..)

Let's say for example that I have 3 robots. Two of those 3 robots produce 1 product in every 10 seconds. Last robot has some major issues, and it takes 20 seconds to produce that 1 product.

So in average of every 4 seconds, one product is made. (20 seconds = 5 products (2+2+1).

So I'm wondering, if there is a function to do this kind of "interval" calculation.

I hope that the title was not too misleading (sorry) and thanks for your help in advance.

 

[Special-K99]

"Two of those 3 robots produce 1 product in every 10 seconds"

So what's the third robot doing, on tea break?

Surely all the robots are working at the same time?

If 1 product gets made by Robots A and B every 10 seconds, does that mean the Robot C has made 1/2 a product after 10 seconds?