`a, 1/2 - 1/( 3 . 7 ) - 1/( 7 . 11 ) - 1/( 11 . 15 ) - 1/( 15 . 19 ) - 1/( 19 . 23 ) - 1/( 23 . 27 )`
`= 1/2 - ( 1/( 3 . 7 ) + 1/( 7 . 11 ) + ..... + 1/( 23 . 27 ) )`
`= 1/2 - ( 4/( 3 . 7 ) + 4/( 7 . 11 ) + .... + 4/( 23 . 27 ) ) . 1/4`
`= 1/2 - ( 1/3 - 1/7 + 1/7 - 1/11 + .... + 1/23 - 1/27 ) . 1/4`
`= 1/2 - ( 1/3 - 1/27 ) . 1/4`
`= 1/2 - 8/27 . 1/4`
`= 1/2 - 2/27`
`= 23/54`
`b, 1 - 1/( 5 . 10 ) - 1/( 10 . 15 ) - .... - 1/( 95 . 100 )`
`= 1 - ( 1/( 5 . 10 ) + 1/( 10 . 15 ) + .... + 1/( 95 . 100 ) )`
`= 1 - ( 5/( 5 . 10 ) + 5/( 10 . 15 ) + .... + 5/( 95 . 100 ) ) . 1/5`
`= 1 - ( 1/5 - 1/10 + 1/10 - 1/15 + .... + 1/95 - 1/100 ) . 1/5`
`= 1 - ( 1/5 - 1/100 ) . 1/5`
`= 1 - 19/100 . 1/5`
`= 1 - 19/500`
`= 481/500`
