How to simplify sum of products boolean expression?
From a Karnaugh map you can get a one group of 4s and three group of 2s. So you can reduce sum of 4 term in which three will have 3 literals and one with 2 literals. By doing it use K-map you will use few 1s for more than one terms so if you don't want to use a K-map just use idempotent rule($x = x + x$) and then simplify.