Salutare!
a) 3 • ( 2 + 5 ) = 3 • 7 = 21
3 • ( 2 + 5 ) = 3 • 2 + 3 • 5 = 6 + 15 = 21
b) 5 • ( 8 - 3 ) = 5 • 5 = 25
5 • ( 8 - 3 ) = 5 • 8 - 5 • 3 = 40 - 15 = 25
c) 4 • ( 4 + 5 ) = 4 • 9 = 36
4 • ( 4 + 5 ) = 4 • 4 + 4 • 5 = 16 + 20 = 36
d) ( 9 - 6 ) • 9 = 3 • 9 = 27
( 9 - 6 ) • 9 = 9 • 9 - 9 • 6 = 81 - 54 = 27