Let the cost of a 2-inch marble be \( x \) cents. Consequently, the cost of a 1-inch marble would be \( x - 30 \) cents.
Rochelle buys 25 1-inch marbles and spends a total of $10, which is equivalent to 1000 cents. Therefore, we can set up the equation for the total cost of the 1-inch marbles:
\[ 25 \times (x - 30) = 1000 \]
Now, let's simplify and solve for \( x \):
\[ 25x - 750 = 1000 \]
Adding 750 to both sides:
\[ 25x = 1750 \]
Now, divide by 25:
\[ x = 70 \]
Thus, the cost of a 2-inch marble is \( x = 70 \) cents.
Now let's verify:
The cost of a 1-inch marble would be:
\[ x - 30 = 70 - 30 = 40 \text{ cents} \]
The total cost for 25 1-inch marbles is:
\[ 25 \times 40 = 1000 \text{ cents} = 10 \text{ dollars} \]
This is consistent with the information provided. Therefore, the cost of a 2-inch marble is:
\[ \boxed{0.70} \]