1. Let's look at the deals at both shops:
- Scrooge's shop: for
c dollars you can buy
n chocolates (quota).
- Market-complex: for
c+3 dollars you can buy
n chocolates (quota).
2. The number of chocolates, n, has to be a whole number. Since Rita bought the chocolates using one-dollar bills, then c and c+3 must be whole numbers too.
3. The market-complex has a deal that gives 2 chocolates fewer per dollar compared to Scrooge's shop. So, \(\frac{n}{c} - \frac{n}{c + 3} = 2\).
4. \(\frac{n}{c} - \frac{n}{c + 3} = 2 = n(\frac{3}{c(c + 3)}) \rightarrow n = \frac{2}{3} * c(c + 3)\). Since n is whole, the right hand side must be whole too and that means c(c + 3) is divisible by 3. This is only possible if c is divisible by 3.
5. Now let's look at some possible cases:
- c = 3. \(n = \frac{2}{3} * 3 * (3 + 3) = 12\). This works.
- c = 6. \(n = \frac{2}{3} * 6 * (6 + 3) = 36\). n must be no more than 20.
- Larger c will also not work since n will then be larger than 20.
6. The deals will now look like:
- Scrooge's shop: for 3 dollars you can buy 12 chocolates.
- Market-complex: for 6 dollars you can buy 12 chocolates.
7. That means Rita bought 12 chocolates and would've payed 6 dollars at the market-complex.
8. Our answer will be:
1 - 12 and 2 - 6.