Marbles come into two sizes:1-inch diameter and 2-inch 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
Let's assume the cost of a 1-inch marble is x cents.
According to the given information, the cost of a 2-inch marble is x + 30 cents.
Rochelle buys 25 1-inch marbles, so she spends 25 * x = 25x cents.
Given that she spends exactly $10, we can write the equation:
25x = 10 * 100 [since 1 dollar = 100 cents]
25x = 1000
x = 1000 / 25
x = 40
Therefore, the cost of a 2-inch marble is x + 30 = 40 + 30 = <<40+30=70>>70 cents. Answer: \boxed{70}.