At Gino's you pay $16 plus $8 per pizza.
At Venetian's you pay $24 plus $6 per pizza.
Let the number of pizzas be x.
At Gino's you pay 16 + 8x
At Venetian's you pay 24 + 6x
Set the two costs equal and solve for x to find out the number of pizzas for which both costs are the same.
16 + 8x = 24 + 6x
16 + 2x = 24
2x = 8
x = 4
Each place gives you a free pizza.
4 pizzas plus the free pizza equals 5 pizzas.
If you need 5 pizzas (including the free one), both parlors cost the same.
If you need fewer than 5 pizzas, use Gino's.
If you need more than 5 pizzas, use Venetian's.
To figure that out you could do 99 minus 38, which would lead you to your answer 61.
That would be:
7,020,032
Hope that helps :)
The total number of keys equals:
12 + 5 + 11 + 2 = 30 keys
The probability to pick a sliver key is:
12/30 = 2/5
The probability to pick a copper key is:
11/30
Hope that helps
