I have 20 Score values:
1, 3, 4, 6, 10, 14, 16, 19, 23, 32, 34, 38, 43, 48, 53, 59, 63, 69, 74, 85.
So, I calculate the Standard Deviation using:
$$ \sigma = \sqrt{\frac{\sum(x-\bar x)^2}n} $$
.. which is 25.4.
Now, from 68-95-99.7% rule there are 68% i.e. at least 13 values from these points would be within 1 Standard deviation?
Is that correct? Then, what are those values? In other words, how many values are in 1 standard deviation and 2 standard deviation?
Calculating the mean as $ 34.7$, you have $12$ values within $1$ standard deviation of the mean, and all $20$ values within $2$ standard deviations.
One standard deviation is from $34.7−25.4$ to $34.7+25.4$, two standard deviations is from $34.7−2 \times 25.4$ to $34.7+2\times25.4$.
You would need more values (say $200$) to get closer to $68 \%$ and $95 \%$, since the normal distribution is a continuous distribution.