We find the z-scores for 10 pounds and for 8 pounds.
The standard deviation is the square root of the variance
 
The z-score for 10 pounds:

The z-score for 8 pounds:

We want to find the fraction, decimal or percent which the shaded area is
of the whole area.  Notice that there is very little shading to the right
of 3.10 because there are very few babies that weigh more than 10 pounds.
In fact you can't even see anything shaded there on the graph below.  But
you see 3.10 marked on the z-score axis (the horizontal axis).

There are two kinds of tables in use today.  Those with both positive and 
negative values in the z-column, and those that have only positive values
in the z-column.
To find the decimal fraction for the shading to the left of z=0.52:
If there are negative values in your z-column, then
find 0.5 in the z-column and go across to 0.02 and read 0.6985.

To find the decimal fraction for the shading to the right of z=3.10:
find 3.1 in the z-column and go across to 0.00 (the next column) and read
0.9990.  That's the area to the left of 3.10. To find the area to the 
right of 3.10 subtract from 1.0000, getting 1.0000-0.9990 = 0.0001
We add the shading left of 0.52 which is 0.6985 to the tiny shading right of
3.10, which is 0.0001 and get 0.6986.
-----------------------------
If there are only positive values in your z-column, then
find 0.5 in the z-column and go across to 0.02 and read 0.1985.
That's the shading right of z=0, so add 0.5000 to that and get 0.1985 
To find the decimal fraction for the shading to the right of z=3.10:
find 3.1 in the z-column and go across to 0.00 (the next column) and read
0.4990.  That's the area between z=0 and z=3.10. To find the area to the 
right of 3.10 subtract from 0.5000, getting 0.5000-0.4990 = 0.0001
We add the shading left of 0.52 which is 0.6985 to the tiny shading right of
3.10, which is 0.0001 and get 0.6986.
Answer: 0.6986
But we can only expect the table to be accurate to two decimal places, so we
should only claim 0.70 as the answer.
The TI-83 or TI-84 gives more accuracy.
0.698184662 
Edwin