1) 21 + 21 + 15 + 17 + 39 = 2 • 21 + 15 + 15 + 2 + 39 = 2 • ( 21 + 15 ) + 41 = 2 • 36 + 41 = 72 + 41 = 113
2) 50 • 16 - 48 • 16 = 16 • ( 50 - 48 ) = 16 • 2 = 32
3) ( 100 + 6 ) • 21 = 100 • 21 + 6 • 21 = 2100 + 6 • ( 20 + 1 ) = 2100 + 6 • 20 + 6 = 2100 + 120 + 6 = 2220 + 6 = 2226