Verified answer

http://www.youtube.com/watch?v=0kXK41r--5U

1)

x = 42'08

x = 4208/100 = 2104/50 = 1052/25 <---- ---- --- -- -

2)

x = 6'343434...

100x = 634'3434...

100x - x = 634'3434 - 6'343434

99x = 628

x = 628/99 <---- ---- --- -- -

3)

x = 6'48787878...

10x = 64'8787878...

1000x = 6487'87878...

1000x - 10x = 6487'87878 - 64'87878

990x = 6423

x = 6423/990 = 2141/330 <---- ---- --- -- -