###Human: Derrick measures the length of his yard. The length of Alex's yard is half the size of Derrick's and the length of Brianne's yard is 6 times the size of Alex's. If Brianne's yard is 30 yards long, how long is Derrick's yard, in yards?, ### Assistant: The length of Alex's yard is 30/6=5 yards.
The length of Derrick's yard is 5*2=10 yards. 
 So the answer is :  10