Suppose I have a cake, which has instructions to heat it for 60 seconds in the microwave. I also have some custard, which has instructions to heat it for 30 seconds in the microwave. For convenience, I put the cake in a bowl, pour the custard over the cake, and then heat them together in one go.
How long should the bowl be placed in the microwave for, such that the custard and cake reach the temperature they would have reached based on their individual instructions? (Let's assume that after heating individually based on their individual instructions, the cake and custard would have reached the same temperature.)
Should it be:
1) 90 seconds?
2) Longer than 90 seconds?
3) Shorter than 90 seconds?