Re: If it takes 3 minutes to boil an egg, how long will it take to boil 3 eggs?

It depends on how big your pot is!

If you are using a small sauce pan that can only hold one egg at a time, it will take about ten minutes - figuring in the time it takes to swap eggs. On a more serious note, you are correct that with a big enough pot of boiling water, the number of eggs shouldn't impact the cooking time for each egg. One exception I can think of would be if the pot were small enough that the three eggs could physically insulate each other from the boiling water to some extent, which could increase your cooking time slightly. Similarly, there are some thermodynamic considerations regarding the heat transfer from the burner to the water to the egg: assuming constant rates of heat transfer per unit volume, increasing the egg/water ratio beyond a threshold limit could lower the amount of heat transfered to each egg, which would also lengthen the cooking time. I would suggest bringing in a dozen eggs and doing the experiment with your students - you might be able to determine what, if any, limits there are to cooking eggs.