Tính bằng cách thuận tiện nhất!:
1987+1992+1997+2002+2007=1987+(1992+1997)+(2002+2007)=1987+3989+4009=1987+7998=9985
1987+1992+1997+2002+2007
=1987+1987+1987+1987+1987+5+5+5+5+5+5+5+5+5+5
=1987*5 + 5*10
=5*(1987+10)
=5*1997
=9985
1987+1992+1997+2002+2007= (2000 - 13)+(2000 - 8)+(2000 - 3)+(2000 + 2)+(2000 + 7) = 5x2000 - (13+8+3-2-7) =
= 10000 - 14 = 9986
1987+1992+1997+2002+2007
=2000-13+2000-8+2000-3+2000+2+2000+7
=2000*5-24+9
=2000*5-15
=10000-15
=9985
Nhớ để cho mik nha❤❤❤.
