Question 877957
This kind of exercise question is too common.
<a href="http://www.algebra.com/tutors/Mixtures%3A-All-in-Symbols.lesson?content_action=show_dev">This is a lesson for it.  http://www.algebra.com/tutors/Mixtures%3A-All-in-Symbols.lesson?content_action=show_dev</a>