Solve for $X$ \[ 2: 5:: x: 10 \]

Step 1 ：This is a proportion problem. The proportion is saying that 2 is to 5 as x is to 10. This can be written as a fraction like this: \( \frac{2}{5} = \frac{x}{10} \).

Step 2 ：To solve for x, we can cross-multiply and then solve for x.

Step 3 ：Let's denote the numbers as follows: num1 = 2, num2 = 5, num3 = 10.

Step 4 ：After cross-multiplying, we find that x = 4.0.

Step 5 ：Final Answer: The solution to the proportion is \( \boxed{4} \).