9999+999+99+9 9999×2222+3333×3334 10000-1-2-3-4-...-80 1+2+3

1个回答

  • ①9999+999+99+9

    =10000+1000+100+9-3

    =11106

    ②9999×2222+3333×3334

    =3333×6666+3333×3334

    =3333×(6666+3334)

    =33330000

    ③10000-1-2-3-4-...-80

    =10000-(1+80)×80÷2

    =10000-3240

    =6760

    ④1+2+3+4+...+78+79+80

    =3240

    ⑤2007*2005/2000

    =(2000+7)×(2000+5)/2000

    = (2000²+12×2000+7×5)/2000

    =2000+12+7/400

    =2012/7/400