[ 20 + 6 + 2 : ( 63 : 9 - 5 ) ] : 9 = [ 20 + 6 + 2 : ( 7 - 5 )] : 9
= ( 20 + 6 + 2 : 2 ) : 9
= ( 20 + 6 + 1 ) : 9
= ( 26 + 1 ) : 9
= 27 : 9
= 3
900 - 90 : 3 - [ 10 - ( 40 - 3 × 11 ) ] = 900 - 30 - [ 10 - ( 40 - 33 ) ]
= 900 - 30 - ( 10 - 7 )
= 900 - 30 - 3
= 870 - 3
= 867
50 + 50 : 5 - 50 = 50 + 10 - 50
= 60 - 50
= 10