12+16+20+...+60
= 12+16+20+24+28+32+36+40+44+48+52+56+60
= ( 12+48)+ ( 16+44) + ( 20+40) + (24+36) + (28+32) + (52 + 56) + 60
= 60 + 60+ 60+ 60 + 60 + 108 + 60
= 6 x 60 +108
= 360+ 108
= 468
12+16+20+...+60
= 12+16+20+24+28+32+36+40+44+48+52+56+60
= ( 12+48)+ ( 16+44) + ( 20+40) + (24+36) + (28+32) + (52 + 56) + 60
= 60 + 60+ 60+ 60 + 60 + 108 + 60
= 6 x 60 +108
= 360+ 108
= 468
Nhé bạn