tolong jawab yang benar ya!!!

1. a x b = 1 x 5 = 5
b x a = 5 x 1 = 5
( a x b ) x c = ( 1 x 5 ) x 4 = 5 x 4 = 20
b x c = 5 x 4 = 20
a x ( b x c ) = 1 x ( 5 x 4 ) = 1 x 20 = 20