=( 100+3)* 12

= 100* 12+3* 12

= 1200+36

= 1236

2.20*55

=20*(50+5)

=20*50+20*5

= 1000+ 100

= 1 100

3.24*205

=24*(200+5)

=24*200+24*5

=4800+ 120

=4920