Since 5 Roberts can manufacture 5 cups in 5 seconds.
It must be that 25 Roberts should be able to manufacture 5 cups in 1 second.
Because as Roberts increase time taken to manufacture same number of cups decreases.
However we are required to find the time taken for 25 cups which is 5 times the original amount therefore it will take 5*1 sec = 5 seconds.

_________________

Think of it this was.
it takes 5 machines 5 second to make 5 cups, so their individual work rate must be 1 cup/5 sec (work= rate*time)
now they asked how much time will 25 robot take for 25 cups. we know the each robot makes 1 cup/5 sec. so it should take them 5 sec to make 25 cups.

Hello from the GRE Prep Club BumpBot!

Thanks to another GRE Prep Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.