tinh nhanh
4823 + 1560 + 5177 + 8440
= ( 4823 + 5177 ) + ( 1560 + 8440 )
= 10000 + 10000
= 10000 x 2
= 20000
10556 + 8074 + 9444 + 926 + 1000
= ( 10556 + 9444 ) + ( 8074 + 926) + 1000
= 20000 + 9000 +1000
= 20000 + 10000
= 30000
576+789+467+111
= ( 789 + 111 ) + 567 + 467
= 900 + 567 + 467
= 1467 + 467
= 1934