3/8 + 2/10 =
3/8 + 1/5 ......here's an easy way once we have reduced both fractions to lowest terms
[ multiply each demoninator by the other fraction's numerator and sum these products ] / [ multiply the denominators] =
[ 8 * 1 + 5 * 3 ] / [ 8 * 5 ] =
[8 + 15 ] / 40 =
23 / 40