You have to make the denominators the same so 1/4 and 3/8, times 1 and 4 by 2 so intead of 1/4 you have 2/8 and 2/8 + 3/8 which makes 5/8, which is a prime number so cannot be simplified
You always have to change the denominators (which are the bottom parts of the fraction) to be the same. To make it simple you do 8 as the denominators, 2 × 4= 8. Now all you have to do is add 2/8 + 3/8= 5/8 Easy as pie! Hope I helped you :)