To determine how many large tanks are needed for 49 sharks, we can start by establishing the ratio of large tanks to sharks.
According to the information provided, there are 4 large tanks for every 28 sharks. We can express this as a ratio:
\[ \frac{4 \text{ tanks}}{28 \text{ sharks}} = \frac{1 \text{ tank}}{7 \text{ sharks}} \]
This means that 1 large tank is required for every 7 sharks.
Now, to find the number of large tanks needed for 49 sharks, we can divide the number of sharks by the number of sharks that can be accommodated per tank:
\[ \text{Tanks needed} = \frac{49 \text{ sharks}}{7 \text{ sharks/tank}} = 7 \text{ tanks} \]
Therefore, the aquarium manager would need 7 large tanks for 49 sharks.