I am trying to learn Standard deviation. I just encountered this problem
I am well aware that standard deviation is the deviation from the mean. I am not able to understand why is 2 and 2.5 multiplied to get x. Shouldn't x be 10 (8 + 2) since its standard deviation is 2?
No, the standard deviation is $2.5$.
And the question states that $x$ is $2$ standard deviations above the mean, which means it is $2 \times 2.5$ units above the mean.
Since the mean is $8$, the answer clearly is $8 + 5$.
The solution is actually correct.