Which of the following represents a correct way to indicate a decimal?

To indicate a decimal correctly, the representation must effectively convey the value and its relationship to the whole number system. Both the first and second choices, 0.5 and .5, are acceptable in standard mathematical notation. These indicate that the value is half of one whole unit. However, option A is often preferred in formal writing and documentation as it clearly shows the leading zero before the decimal point, emphasizing the value being less than one.

The leading zero can aid clarity for readers, making it immediately apparent that the number is indeed a decimal value, particularly in contexts like medication dosage where precision is crucial.

While D (5.0) shows the decimal point and indicates a whole number with a decimal, it does not lean into indicating a fraction of a whole. It simply reinforces that the value is five, rather than explicitly showing it is half or another fraction less than one.

Overall, the reason A is considered the best answer is its balance of clarity and adherence to conventional standards in representing decimals, ensuring that the number is readily understood in the context of medication calculations.