What is one half plus one fifth?

You first need to break the question down into fractions that can be added together, thus:-

one half = five tenths

one fifth = two tenths

then do the addition

five tenths + two tenths = seven tenths
Solving 1/2 + 1/5...

1/2 = 5/10

1/5 = 2/10

5/10 + 2/10 = 7/10