well if you are talking about equivalent fractions then it is easy! So what you do to the numerator you do to the denominator and what you do to the denominator you do to the numerator. The numerator is the top part of a fraction and a denominator is the bottom part of a fraction. Because 1/5 is in simplest form you can multiply it by any number. Like 1/5=2/10. What I did for that is I multiplied the numerator and the denominator by 2. I think you can think of more. So this is why you need to memorize your multiplication tables.
1/5
1/5
1/2 and 5/10
1/5, 3/15
two equivalent fractions for 5 over 15 = 1/3, 10/30
Halfway between two fractions would be the average of the two fractions, so add the two fractions together and divide by two! Let's take 1/2 and 3/4 as an example. Add 1/2 (or 2/4) and 3/4 and you get 5/4. Now divide by two ( or multiply the bottom part by two) and your answer is 5/8!
1/3 + 1/2
1/5 and 4/20
1/2 and 2/4
1/3 or 10/30
2/10, 3/15
2/10, 1/5