Question

巧算小学数学分数题，请教一下。

3/10+3/40+3/88+3/154+3/238+3/340=?

Answer 1

=3/2*5+3/5*8+3/8*11+3/11*14+3/14*17+3/17*20

=1/2 - 1/5 + 1/5 - 1/8 + ... + 1/17 - 1/20

= 1/2- 1/20

= 9/20

Answer 2

1/(2*5)=1/3*(1/2-1/5)
1/(5*8)=1/3*(1/5-1/8)
......
3/10+3/40+3/88+3/154+3/238+3/340
=3/(2*5)+3/(5*8)+3/(8*11)+3/(11*14)+3/(14*17)+3/(17*20）
=(1/2-1/5)+(1/5-1/8)+...+(1/17-1/20)
=1/2-1/5+1/5-1/8+...+1/17-1/20
=1/2-1/20
=9/20

Answer 3

3/10+3/40+3/88+3/154+3/238+3/340
=3/(2*5)+3/(5*8)+3/(8*11)+3/(11*14)+3/(14*17)+3/(17*20)
=1/2-1/20
=9/20

Answer 4

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