100x20+20x900
=(100+900)x20
=1000x20
=20000
=20000
ung ho minh nha 
chiến binh ngân nga!!!
100 x 20 + 20 x 900
= 20 x (100 + 900)
= 20 x 1000
= 20000
C2 :
100 x 20 + 20 x 900
= 2000 + 18000
= 20000
100x20+20x900
=(100+900)x20
=1000x20
=20000
100 x 20 + 20 x 900 = 20 x 900 + 100 = 20 x 1000 = 20000 k nha
=20\(\times\)(100+900)
=20\(\times\)1000
=20000
