To find out how many square miles will be in each family garden, you need to divide the total area of the field by the number of gardens.
- Total Area of the Field: \( 3.9 \) square miles
- Number of Gardens: \( 1.3 \times 10^3 = 1300 \)
Now, divide the total area by the number of gardens:
\[ \text{Area per garden} = \frac{3.9 \text{ square miles}}{1300 \text{ gardens}} \]
Calculating this gives:
\[ \text{Area per garden} = \frac{3.9}{1300} \text{ square miles} \]
To simplify \( \frac{3.9}{1300} \):
- Calculate \( 3.9 \div 1300 \):
\[ 3.9 \div 1300 = 0.003 \]
Now convert \( 0.003 \) to scientific notation:
\[ 0.003 = 3.0 \times 10^{-3} \]
So, the area in each family garden in scientific notation is:
\[ \boxed{3.0 \times 10^{-3}} \text{ square miles} \]