Then formula one. . . .
You can multiply the following number by 3. .
( 1- 1/2)+( 1/2- 1/3)+( 1/3- 1/4)。 . . . . . . . . . . . ( 1/2007- 1/2008)
= 1- 1/2008
Just do it.
Calculate your own answers and learn to use them.