Lizzie gets $$20 \%$$ on a $$10$$-problem test, $$80 \%$$ on a $$20$$-problem test and $$90 \%$$ on a $$30$$-problem test. If the three tests are combined into one $$60$$-problem test, what percentage is her overall score? 
Overseas Competition->Knowledge Point->Word Problem Modules->Solving Problems Involving Fractions and Percentages->Finding the Rate