Bài `1 :`
`A = ( - 1/4 + 7/35 - 5/3 ) - ( - 15/12 + 6/11 - 48/49 )`
`A = - 1/4 + 7/35 - 5/3 + 15/12 - 6/11 + 48/49`
`A = - 1/4 + 1/5 - 5/3 + 5/4 - 6/11 + 48/49`
`A = ( - 1/4 + 5/4 ) - ( 5/3 + 6/11 ) + 48/49 + 1/5`
`A = 1 - 2 + 48/49 + 1/5`
`A = - 1 + 48/49 + 1/5`
`A = ( - 1 )/49 + 1/5`
`A = 44/245`
Vậy `, A = 44/245 .`
Bài `2 :`
`B = ( 1/98 + 1/99 - 1/100 ) . ( 1/15 - 1/9 + 2/45 )`
`B = ( 1/98 + 1/99 - 1/100 ) : ( 3/45 - 5/45 + 2/45 )`
`B = ( 1/98 + 1/99 - 1/100 ) : ( ( - 2 )/45 + 2/45 )`
`B = ( 1/98 + 1/99 - 1/100 ) : 0`
`B = 0`
Vậy `, B = 0 .`