Here is one answer I found about 10/10/80 loan: http://answers.yahoo.com/question/index?qid=20111016153518AA9w8MG

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10% down
80% will be for regular mortgage
10% for a small mortgage until you pay off the PMI balance

You pay PMI - private mortgage insurance if you don't have 20% to put down on a home. This can add thousands of dollars to a mortgage. It's not tax deductible, an does not go towards principal or interest. So it is important to pay it off aggressively first.

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I assume 5/15/80 can be interpreted the same way.