"How much is a half plus a third (1/2 + 1/3)?”
Nic Martinek (age 8): "One half is the same as 1 1/2 thirds. So, 1 1/2 thirds plus 1 third is 2 1/2 thirds. Doubled up, that makes 5/6.
This is what is called “number sense” approach (see picture below).
And yes, you can solve it by using algorithm as well – convert those fractions into 3/6 + 2/6 and you'll get 5/6.