Hi! Since this is a question about the Math Challenge II-A books/class, it's probably best on the forum on the classes.areteem.org site, so I posted my reply there. Please click here to see some hints/thoughts on the these problems.
Discussion Forum
AMC 10 Winter 4.27, 4.28 4.30
Re: AMC 10 Winter 4.27, 4.28 4.30