Simplifying answers.

We are working on solving proportions. Why do we have to simplify answers on some questions and not others, in the same lesson? For instance fractions and decimals. Sometimes just 10 wont work and you have to put 10/1 as the answer (or 20/2) and vice versa. Both answers are correct and even the supporting videos simplify the answers by working out 20/2 as 10, but it wont allow that simplified answer as an answer sometimes. Weve encountered it multiple times in math. An example lesson is 9/10 = 10/k. The answer is 100/9, but sometimes the answer is 11.11. Both answers are correct, but we may get it wrong because sometimes it wants the fraction, and sometimes it wants the simplified answer. k=100/9 and 11.11. Am i missing something? Am i missing a rule that says when we use the fraction and when we use the decimal/whole number?