To find the approximate weight of the water in an Olympic-sized swimming pool, we can use the following calculation:
- The volume of the swimming pool is \( 6.6 \times 10^5 \) gallons.
- Each gallon of water weighs about 8.3 lbs.
Now, we calculate the total weight:
\[ \text{Total weight} = \text{Volume} \times \text{Weight per gallon} \]
\[ \text{Total weight} = (6.6 \times 10^5 \text{ gallons}) \times (8.3 \text{ lb/gallon}) \]
Performing the multiplication:
\[ \text{Total weight} = 6.6 \times 8.3 \times 10^5 \]
Calculating \( 6.6 \times 8.3 \):
\[ 6.6 \times 8.3 = 54.78 \]
Thus, we have:
\[ \text{Total weight} = 54.78 \times 10^5 \text{ lb} \]
In scientific notation, we should express this with a single digit before the decimal place:
\[ 54.78 \times 10^5 \text{ lb} = 5.478 \times 10^6 \text{ lb} \]
So the approximate weight of the water in an Olympic-sized swimming pool is:
\[ \boxed{5.478 \times 10^6 \text{ lb}} \]