Since 111, 777, and 999 are all bigger than 20, make them smaller. Take out one 1, two 7, and two 9 (5 numbers): 11 + 7 + 9 ≠ 20 (it equals 27). Now take out number 7. (If you take out number 1 [1+7+9=17, not 20] and of you take out number 9 [11+7=18, not 20].
11 + 9 = 20 (you took out numbers: 1, 7, 7, 7, 9 and 9 [6 numbers]).
