OK girls & boys-
It works because ANYTIME you take a 2 digit number and subtract the sum of those digits from the original number, the remainder (remember that term

) will be a number divisibwe by 9. Go look at the chart....all numbers eligible to be remainders and divisible by 9 have the same symbol.
36 minus 9 (the sum of 3+6) = 27
47 minus 11 (the sum of 4+7) = 36
see..now you are a math whiz too ! Go amaze your friends :p