a) 35 . 18 - 5 . 7. 28
= 35 .18 - 35 . 28
= 35 . (18-28)
= 35 . - 10
= -350
b) 24 . (16-5) - 16 . (24-5)
= 24 . 16 - 24 . 5 - 16 . 24 + 16 . 5
= -24 . 5 + 16 . 5
= 5 . (-24+16)
= 5 . -8
= -40
c) 31 . (-18) + 31 . (-81) - 31
= 31 . (- 18 + -81 + -1)
= 31. -100
= -3100
d) -12 . 47 + -12 . 52 + -12
= -12 . (47+52+1)
= -12 . 100
= -1200
e) 13 . (23+22) - 3 . (17+28)
= 13 . 45 - 3 . 45
= 45 . (13-3)
= 45 . 10
= 450