Question

小学教材全练数学6年级下册中，（1）1994+1/1992*1992/1993（2）9999*2222+3333*3334

（3）1/2+1/6+1/12+1/20+1/30+1/42（4）1988+1989*1987/1988*1989-1

Answer 1

1 1994+1/1992*1992/1993=1994+1/1993=1994又1/1993

2 9999×2222+3333×3334=9999×2222+3333×3333+3333=9999×2222+9999×1111+3333=9999×3333+3333=（9999+1）×3333=33330000

3 1/2+1/6+1/12+1/20+1/30+1/42=1/(1×2)+1/(2×3)+1/(3×4)+......+1/（6×7）=1-1/2+1/2-1/3+1/3+。。。。。。+1/6-1/7=1-1/7=6/7
4 1988+1989*1987/1988*1989-1=1988+1987/1988-1=1987又1987/1988

Answer 2

1）1994+1/1992*1992/1993=1994+1/1993=1994又1/1993
2）9999*2222+3333*3334=9999*2222+3333*3333+3333
=9999*2222+9999*1111+3333
=9999*3333+3333
=（9999+1）*3333
=33330000
3）1/2+1/6+1/12+1/20+1/30+1/42 1/2=1-1/2,1/6=1/2-1/3，……
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7
=1-1/7
=6/7
4）1988+1989*1987/1988*1989-1=1988+1987/1988-1=1989又1987/1988

Answer 3

（1）1994+1/1992*1992/1993=1994+1/1993=1994又1/1993
（2）9999*2222+3333*3334 =3333*（3*2222+1*3334）=3333*10000=33330000
（3）1/2+1/6+1/12+1/20+1/30+1/42=1/2+1/（2*3）+1/（3*4）+1/（4*5）+1/（5*6）+1/（6*7）
=1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7=1/2-1/7=5/14
1989*1987
（4）1988+1989*1987/1988*1989-1=1988+---------------------1=1988+1987/1988-1
=1988-1/1988=1987又1987/1988
1988*1989

Answer 4

1）1994+1/1992*1992/1993=1994+1/1993=1994又1/1993
2）9999*2222+3333*3334=9999*2222+3333*3333+3333
=9999*2222+9999*1111+3333
=9999*3333+3333
=（9999+1）*3333
=33330000
3）1/2+1/6+1/12+1/20+1/30+1/42 1/2=1-1/2,1/6=1/2-1/3，……
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7
=1-1/7
=6/7

Answer 5

1/2+1/6+1/12+1/20+1/30+1/42
=(1-1/2 )+(1/2 -1/3 )+( 1/3 -1/4)+(1/4 -1/5 )+(1/5 -1/6 )+(1/6 -1/7 )
=6/7

1988+1989*1987/1988*1989-1
=1988+1987/1988-1
=1988-1/1988
=1987/1988