Marbles come in 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 the cost of a 2-inch marble be $x.
Then the cost of a 1-inch marble is $x - $0.30.
Rochelle buys 25 1-inch marbles for a total cost of 25 * ($x - $0.30).
Since Rochelle spends exactly $10, we can set up the equation 25 * ($x - $0.30) = $10.
Simplifying the equation, we get 25x - 7.5 = 10.
Adding 7.5 to both sides of the equation, we get 25x = 17.5.
Dividing both sides of the equation by 25, we get x = 0.7.
Therefore, the cost of a 2-inch marble is $0.7. Answer: \boxed{0.7}.