For this, you need to find the lowest common multiple of the denominators, 2 and 8, which is 8 (since 8 is divisible by 2). 8 divided by 2 is 4, so if you multiply both numerator and denominator of 1/2 by 4. Once you have a common denominator, you can then add the numerators together:
1/2 + 1/8
=(1x4) / (2x4) + 1/8
=4/8 + 1/8
= 5/8
Which is the answer.