As general rule, the strong beat in Latin music is at beat 1. But in the CD "Rhythm of Results" of Ton Greten (http://www.dsi-london.com/site/?action=prod_page&pid=9163&cat_id=13&type=18&sub_id) he said that the strong beat in Rumba is in beat 4 (it is syncopated!!!). I also do not know why Walter Laid said in his book that Rumba has beat 4 strong)

Therefore what is the exact music of International Rumba (used in WDC and WDSF contests)? Rumba with strong beat in beat 1 or Rumba with strong beat in beat 4? If they use beat 4 strong, what is the reason?

Can anyone know it clearly? And how about music rhythm of Chacha in WDC & WDSF?

Dance Lover. There is a musical accent in the Cha Cha on beat 1.
In the Rumba. It is possible with some that the Rumbas they dance to are not true Rumbas. The predominent percussive accent is on beat 4 in a Rumba.

You mean that the true Rumba has strong accent on beat 4. But can you let me know it is syncopated (strong beat at 2 and 4) or it is normal with extra beat in 4 (strong beat at 1,3,4)?
Do you have any information about strong beat at 2 in Rumba except Walter Laird book?
Thank in advance