21/5.2
because in order to get mean you have to add all the numbers up and divide by the amount you added so 20+28+26+26+30+24+25+26+28+27= 210 divide by 10= 21
in order to get mad you take all the numbers and subtract them from the mean (what ever you get make sure the number is positive) so 21-20=1 28-21=7 and so on then add up the numbers and divide again to get 52 divide that by 10 and you get 5.2
because it is means to mad ratio the answer is 21/5.2