B16:
a) 42+257+43+158
=(42+158)+(257+43)
=200+300
=500
b) 205+(2003+95)
=205+2003+95
=(205+95)+2003
=300+2003
=2303
c) 283+119+37+17+81
=(283+17)+(119+81)+37
=300+200+37
=537
d) (25 x 35) x 40
=(25 x 4) x (35 x 10)
=100 x 350
=35000
e) (125 x 9)80
=(125 x8) x(9.10)
=1000 x 90
=90000
f) 11+12+13+...+28+29
=[(29-11):1+1] x[(29+11):2]
=19 x20
=380
B17:
a) 92 x 17+83 x92
=92 x (17+83)
=92 x100
=9200
b) 108 x12+25.92+13.108
=108 x (12+13)+25.92
=108 x 25+25.92
=25 x (108+92)
=25x 200
=5000
c) 1+3+5+...+39
=[(39-1):2+1] x[(39+1):2]
=20x 20
=400
d) 2+7+12+17+....+62
=[(62-2):5+1] x[(62+2):2]
=13 x 32
=416