The ratio of $50$ to $20$ can be simplified to $5:2$.

To simplify a ratio, you must divide both numbers by their greatest common divisor (GCD). In this case, the GCD of $50$ and $20$ is $10$. When we divide $50$ by $10$, we obtain $5$. Likewise, dividing $20$ by $10$ gives us $2$. Thus, the ratio $50:20$ simplifies to $5:2$.

Ratios serve as a means to compare two quantities, illustrating how many times one value is contained within the other or vice versa. Specifically, the ratio $5:2$ indicates that for every $5$ units of the first quantity, there are $2$ units of the second quantity. Simplifying ratios not only makes them easier to understand but also facilitates calculations, particularly in problems involving proportions and scaling.

Mastering the skill of simplifying ratios is essential in GCSE Maths, as it applies to various topics such as proportions, scaling, and practical scenarios like cooking or mixing solutions. Always remember to determine the GCD of the numbers involved to accurately simplify the ratio. This approach guarantees that the ratio is expressed in its simplest form, making it easier to interpret and apply in further calculations.