Which of the following is NOT a recommended way of writing ratios?

The correct understanding of the recommended ways to write ratios recognizes that all provided formats convey the same relationship between two quantities. However, in specific contexts, certain formats may be more common or preferred than others.

The format "2:1" represents a ratio that is clear and concise, making it easily understood. Similarly, "1:2" displays the relationship effectively. "2 to 1" is also a standard way of expressing a ratio in descriptive text. Conversely, "2/1" is typically associated with fractions or division, which can lead to confusion regarding whether it's intended as a ratio or a simple mathematical fraction.

In many formal or educational contexts, the latter format may be less favored compared to the more clear forms like "2:1" or "2 to 1." Thus, while all formats can technically express a ratio, "2/1" stands out as potentially less recommended in traditional ratio expression scenarios, depending on practices in different settings.