We have our needed parameters as:
MTU = 100 bytes
The Size of IP header = 20 bytes
size of data that can be transmitted in one fragment is given as = 100 – 20 = 80 bytes
Size of data to be transmitted = Size of datagram – size of header = 1000 – 20 = 980 bytes
Now, we have a datagram of size 1000 bytes.
So, we need ceil(980/80) = 13 fragments.
This simply means there will be 13 fragments of the datagram.