Answer:

Now we can find the second moment with this formula:

And replacing we got:

The variance would be given by:
![Var(X) =E(X^2) -[E(X)]^2 = 21.4 -[3.8]^2 = 6.96](https://tex.z-dn.net/?f=%20Var%28X%29%20%3DE%28X%5E2%29%20-%5BE%28X%29%5D%5E2%20%3D%2021.4%20-%5B3.8%5D%5E2%20%3D%206.96)
And the deviation would be:

Step-by-step explanation:
For this case we have the following distribution given:
X 1 2 7
P(X) 1/5 2/5 2/5
We need to begin finding the mean with this formula:

And replacing we got:

Now we can find the second moment with this formula:

And replacing we got:

The variance would be given by:
![Var(X) =E(X^2) -[E(X)]^2 = 21.4 -[3.8]^2 = 6.96](https://tex.z-dn.net/?f=%20Var%28X%29%20%3DE%28X%5E2%29%20-%5BE%28X%29%5D%5E2%20%3D%2021.4%20-%5B3.8%5D%5E2%20%3D%206.96)
And the deviation would be:
