Vinay,
is this what you mean?
= If([Total Registrations]=0;"0" ForAll ([Acct Id]) ;
If([Total Registrations]> 0 And [Total Registrations] < 5;"1-4" ForAll ([Acct Id]);
If([Total Registrations]> 4 And [Total Registrations] <11 ;"5-10" ForAll ([Acct Id]);
If([Total Registrations]> 10 And [Total Registrations] < 21 ;"11-20" ForAll ([Acct Id]);
If([Total Registrations]>= 21 ;"21+" ForAll ([Acct Id]);
"N/A")))))
I tired both FoirEch abd ForAll but it doesn't make any differentce.