Marbles come in two sizes: 1- inch diameter and 2-invhe diameter. The 1-inch diameter marbles cost 30 cents less than the 2- inch marbles. Rochelle buys 25 1-inch marbles for her science project and spends exactly $10. Find the cost of a 2-inch marble?

Answer 1

Let's assume the cost of a 2-inch marble is x cents.
The cost of a 1-inch marble is then (x - 30) cents.
Rochelle buys 25 1-inch marbles, so she spends a total of 25 * (x - 30) cents.
This is equal to $10, which is 1000 cents. So we have the equation:
25 * (x - 30) = 1000
Dividing both sides by 25, we get:
x - 30 = 40
Adding 30 to both sides, we get:
x = 70
Therefore, the cost of a 2-inch marble is 70 cents. Answer: \boxed{70}.