the incubation time for rhode island red chicks is normally distributed with mean of 30 days and standard deviation of approximately 2 days.

Here is a pic

Here the probability is calculated to be 2.14 %.  It would be a little more accurate than my 2.35%

Using this percentage  the answer would be 0.0214*1000=21.4 = 21 chicks

30-3*2=24 so    24 is 3 standard deviations below the mean

30-3*3-26  so     26 is 2 standard deviations below the mean

Prob  of being in this area is approx  (99.7-95)/2 percent 

$${\frac{\left({\mathtt{99.7}}{\mathtt{\,-\,}}{\mathtt{95}}\right)}{{\mathtt{2}}}} = {\frac{{\mathtt{47}}}{{\mathtt{20}}}} = {\mathtt{2.35}}$$      percent

$${\frac{{\mathtt{2.35}}}{{\mathtt{100}}}}{\mathtt{\,\times\,}}{\mathtt{1\,000}} = {\frac{{\mathtt{47}}}{{\mathtt{2}}}} = {\mathtt{23.5}}$$      

23.5 chick.   I suppose I should round that to approx   24 chicks.   :)