Sorry if this is a stupid question but please give me some help
How would you know the standard deviation of a graph just from looking at it, I get that the mean is 10 but how is the standard deviation 4/3?
I guess there is no actual method to deduct the standard deviation just by observing the graph IMO. However, you can use following trick to roughly estimate the SD from a Normal distribution.
It is known that where and are the mean and SD.
Basically, if you could guess where the tail almost become zero from the figure, it helps you to make a rough estimation.
In you figure, and tails almost disappear at and . Therefore, $10+3\sigma=14$ and $10-3\sigma=6$ need to satisfied.
That says $\sigma \approx 4/3$.