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

The correct answer is based on the conventions used to express ratios clearly and consistently. While all the expressions given represent a ratio, one of them is less commonly recommended in formal contexts.

The notation "B. 2:1" is a standard and widely accepted way to write ratios, as it uses a colon to separate the two quantities. The choice "C. 2 to 1" is also a valid expression and is often used in verbal contexts, making it understandable in conversation. The form "D. 2/1" is a fractional representation, which is also acceptable mathematically, as it implies a ratio of two parts to one part.

The choice "A. 1:2" represents the ratio the same way as option B does, just flipped. However, when looking for the option that might be least fitting in certain formal mathematical or scientific contexts, "B" casually implies a ratio of 2 in context but does not maintain consistency in format like the others.

Therefore, while all forms express ratios, the one that may not align with the recommended standard in formal writing is B. The commonly accepted ways and clear representations in ratio context lean towards the use of colons or the phrase form over a simple number representation