`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/( 11.15) + 1/( 15 . 19) + 1/( 19 . 23) + 1/( 23 . 27))`
`= 1/2 - [1/4 . (4/(3.7) + 4/( 7.11) + 4/( 11.15) + 4/( 15 . 19) + 4/( 19 . 23) + 4/( 23 . 27))]`
`= 1/2 - [ 1/4 . ( 1/3 - 1/7 + 1/7 - 1/11 + 1/11 - 1/15 + 1/15 - 1/19 + 1/19 - 1/23 + 1/23 - 1/27)]`
`= 1/2 - [ 1/4 . ( 1/3 - 1/27)]`
`= 1/2 - ( 1/4 . 8/27)`
`= 1/2 - 2/27`
`= 23/54`
