How do you simplify # 1/5 + 3/5#?
The top number of a fraction (numerator) is the count.
The bottom number (denominator) is the size indicator of what you are counting. In this case the size indicator is 5 which means it takes 5 of what you are counting to make a complete 1 of something.
As the 'size indicators' (denominators) are the same we can directly add the counts (numerators).
Suppose we had:
What we a counting is all of size type 10 (have the same denominator of 10)
As they are all of the same size it is perfectly correct to write it as:
This simply means that every one of what we are counting is size type 10. If you like: they are sharing the one size indicator notation(denominator of 10).