There are no breakfast facilities and you and your friend are in a hurry to get on your way, but will not leave the room until after having a cup of tea.
Knowing the hotel, you and your friend have brought your own cups, teabags and mini immersion heaters to boil water in the cups. You both drink tea with neither sugar nor milk.
In order to get on your way as quickly as possible, you and your friend seek the quickest way to boil the water, make the tea, drink it and get out the door in the shortest time.
You announce that it is quicker to fill both cups with water and place an immersion heater in each simultaneously - thereby boiling both cups simultaneously. Your friend claims that it is quicker to place both heaters in one cup and then once boiled heat the second cup (let's assume that we don't care that the two cups are ready at slightly different times - maybe one of you prefers tea at a hotter drinking temperature than the other).
Which of you is correct? Will the elapsed time for boiling two cups simultaneously be shorter or longer than boiling the two cups sequentially? Does it make no difference?
Reasons for your response in the comment section below.