The mean of 100 numerical observation is 51.18 what is the value of the sum of all 100 numbers

The "mean" is the same thing as the "average".

To get the average, you add up all the numbers on the list,
then divide the big sum by the number of items on the list.

If there are 100 numbers on the list, then in order to find their average,
you would add up all 100 numbers, then divide the big sum by 100.

If you wound up with an average of 51.18, then you must have had
5,118 just before you divided it by 100.  So the big sum is 5,118.

We are told that each person flips a coin 200 times. We know that a coin has two options when heads or tails fall, therefore, the results between Amir and Marvin are compared with the number of heads and the number of tails that each one obtained.

The theoretical probability says that out of 200 times a coin is flipped by having 50% heads or tails come out, 100 must be heads and 100 must be tails, theoretically obviously speaking.

Therefore with these values it would be the comparison.