Đáp án:
`3/20`
Giải thích các bước giải:
`A=1/10+1/40+1/88+1/154+1/238+1/340`
`=>A=1/2.5+1/5.8+1/8.11+1/11.14+1/14.17+1/17.20`
`=>3A=3.(1/2.5+1/5.8+1/8.11+1/11.14+1/14.17+1/17.20)`
`=>3A=3/2.5+3/5.8+3/8.11+3/11.14+3/14.17+3/17.20`
`=>3A=(5-2)/2.5+(8-5)/5.8+(14-11)/11.14+(17-14)/14.17+(20-17)/17.20`
`=>3A=1/2-1/5+1/5-1/8+1/8-1/11+1/11-1/14+1/17+1/17-1/20`
`=>3A=1/2-1/20`
`=>3A=9/20`
`=>A=9/20:3`
`=>A=3/20`
Vậy biểu thức có giá trị là `3/20`.
