Answer:
Minimun amount = $95,48
Step-by-step explanation:
We need to buy the book that costs 12 galleons, 16 sickles, 25 knuts.
At the bank we need to exchange our dollars. We know that:
1 galleon = $7,35
And:
1 galleon = 17 sickles
1 sickle = 29 knuts
First we use a rule of three to convert everything to galleons:
1 galleon = 17 sickles ⇒ 1 sickle = 1/17 galleons
1 sickle = 1/17 galleons = 29 knuts ⇒ 1 knut = 1/493
And now we need to convert every wizarding money to dollars by using our reference above:
1 galleon = $7,35
1 sickle = 1/17 galleons = $7,35 / 17 ≅ $0,4323
1 knut = 1/493 galleons = $7,35 / 493 ≅ $0,0149
Finally we calculate the cost of the book:
Galleons: 12 x $7,35 = $88,2
Sickles: 16 x $0,4323 = $6,91
Knuts: 25 x $0,0149 = $0,37
Cost of the book = $88,2 + $6,91 + $0,37 = $95,48
So this is the minimun amount of dollars you need to exchange to purchase the book.