Mixture problems don't seem to show up as often nowadays as they used to. I think we've changed the algebra curriculum to pave way for the 7th and 8th graders ... I'm thinking that these questions were deemed irrelevant or too difficult.
Standard instructions for this series: No calculator allowed. Express answers in reduced form. Rationalize denominators. Radicals must be reduced. All numbers are base ten unless otherwise specified. Do not approximate radicals or π. Leave such answers as 1025π or √39, for example. Source: UVM Math Contest
answer 14 and answer 28.