Đáp án:
`↓↓↓`
Giải thích các bước giải:
`A=1/12+1/20+1/30+...+1/9702`
`A=1/3.4+1/4.5+1/5.6+...+1/98.99`
`A=1/3-1/4+1/4-1/5+...+1/98-1/99`
`A=1/3-(1/4-1/4+1/5-...-1/98+1/99)`
`A=1/3-1/99`
`A=32/99`
------------
`B=1/2.5+1/5.8+1/8.11+....+1/92.95+1/95.98`
`B=1/3[1/2-(1/5-1/5+1/8-1/8+1/11-...-1/95+1/98)]`
`B=1/3(1/2-1/98)`
`B=1/3×24/49`
`B=8/49`