If the sum of two numbers is 100 and their difference is 50, the ratio of the two numbers will be

The correct answer is (c).

Let $x$ and $y$ be the two numbers. We know that $x+y=100$ and $x-y=50$. Adding these two equations, we get $2x=150$, so $x=75$. Substituting this into $x+y=100$, we get $75+y=100$, so $y=25$. Therefore, the ratio of the two numbers is $\frac{x}{y}=\frac{75}{25}=\boxed{3:1}$.

Option (a) is incorrect because the sum of the two numbers is 100, not 50. Option (b) is incorrect because the difference of the two numbers is 50, not 25. Option (d) is incorrect because the ratio of the two numbers is 3:1, not 5:1.