question about dns query distribution

[M. Meadows]

Recently noticed that for 2 nameservers ns1.tbd.com and ns2.tbd.com (names are changed to protect the innocent) the first nameserver consistently receives twice as many queries as the 2nd nameserver. 
Who can tell me why queries are distributed this way? 
Any ideas? 
I assume it's something relatively simple. 
Thank you.
Marty

 		 	   		  
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