Nandini makes 'halwa' one evening and divides it into four equal portions for her family of four. However, just as they are about to eat it, an unexpected guest arrives and Nandini has to now re-divide the halwa into five equal portions. By what percentage has each family member's share reduced due to this?

5%

Step-by-step explanation:

We know that when there are four people, then each person gets 25% of the halwa. However, when the fifth person comes, they have everyone including the guest get 20% of the halwa. In this way, the original four people are losing 5% of their halwa in order for the fifth person to get his piece