Harry Potter would like to purchase a new owl which cost him 2 Galleons, a Sickle, and 5 Knuts. There are 23 Knuts in a Sickle and 17 Sickles in a Galleon. He currently has no money, but has many potions, each of which are worth 9 Knuts. How many potions does he have to exhange to buy this new owl?

[i]2015 CCA Math Bonanza Individual Round #7[/i]
1. **Convert the cost of the owl into Knuts:**
   - Given: 1 Galleon = 17 Sickles and 1 Sickle = 23 Knuts.
   - Therefore, 1 Galleon = \( 17 \times 23 = 391 \) Knuts.
   - The cost of the owl is 2 Galleons, 1 Sickle, and 5 Knuts.
   - Convert 2 Galleons to Knuts: \( 2 \times 391 = 782 \) Knuts.
   - Convert 1 Sickle to Knuts: \( 1 \times 23 = 23 \) Knuts.
   - Add the 5 Knuts directly.

2. **Sum the total Knuts:**
   \[
   782 \text{ Knuts} + 23 \text{ Knuts} + 5 \text{ Knuts} = 810 \text{ Knuts}
   \]

3. **Determine the number of potions needed:**
   - Each potion is worth 9 Knuts.
   - To find the number of potions needed, divide the total Knuts by the value of each potion:
   \[
   \frac{810 \text{ Knuts}}{9 \text{ Knuts/potion}} = 90 \text{ potions}
   \]

The final answer is \(\boxed{90}\).