=2+2+...+2 (25 binary)

=25*2

=50

2004-200 1+ 1998- 1995.。 . . . . . + 12-9+6-3

=3+3+...+3 (334 3s)

=334*3

= 1002

5* 1/9+9* 1/ 13+ 13* 1/ 17+。 . . . . . . . . + 10 1* 1/ 105

I can't do it. Is the topic right?

I guess the topic is this:

1/5* 1/9+ 1/9* 1/ 13+ 1/ 13* 1/ 17+。 . . . . . . . . + 1/ 10 1* 1/ 105

= 1/4( 1/5- 1/9+ 1/9- 1/ 13+...+ 1/ 10 1- 1/ 105)

= 1/4*( 1/5- 1/ 105)

= 1/2 1

1/20+ 1/30+ 1/42+ 1/56+ 1/72+ 1/90

= 1/4- 1/5+ 1/5- 1/6+ 1/6- 1/7+ 1/7- 1/8+ 1/8- 1/9+ 1/9- 1/ 10

= 1/4- 1/ 10

=3/20