Answer:
6 legs
Step-by-step explanation:
1 grandpa: the grandpa is the father (dad number 1) of one of those seated.
Son number 1: The grandpa has a son.
Son number 2: The grandpa's son also has a son.
This makes him a dad (Dad number 2).
The son of the grandpa's child is the grandpa's grandson.
We can say from the above, a man (grandpa) has a Son and a grandson.
Each person has two legs.
For 3 persons, we would have = 2×3 = 6legs
Therefore a 4 legged table with 1 grandpa, 2 dads, 2 sons and a grandson have 6 legs under the table.