A student answers a problem with the fraction 3/15. Why is this considered incorrect?

The fraction 3/15 is considered incorrect because it is not simplified. Simplifying a fraction involves reducing it to its lowest terms, which makes it easier to understand and work with. In this case, both the numerator (3) and the denominator (15) share a common factor of 3. When we divide both the numerator and denominator by 3, we reduce the fraction to 1/5, which is its simplest form. Therefore, the original fraction of 3/15 is not in its most simplified state, making it appear less acceptable in most mathematical contexts. Simplification is crucial for clarity and accuracy in mathematics, as it allows for easier calculations and comparisons between fractions.