`B= 2/1.4 + 2/4.7 + 2/7.10 +...+ 2/97.100`
`B: 2 = 1/1.4 + 1/4.7 + 1/7.10 +...+ 1/97.100`
`B: 2.3 = 3/1.4 + 3/4.7 + 3/7.10 +...+ 3/97.100`
`B : 2 .3 = 1- 1/4 + 1/4 -1/7 + 1/7- 1/10 -...- 1/97-1/100`
`B:2 .3= 1- 1/100`
`B: 2.3 = 99/100`
`B= 99/100 : 3 .2`
`B= 99/100 . 1/3 .2`
`B= 33/100 . 2`
`B= 33/50`
Vậy `B= 33/50`