Answer: 540
Step-by-step explanation:
Given : The owner of a stereo store wants to advertise that he has many different sound systems in stock.
Number of different CD​ players =6
Number of different receivers= 10
Number of  different speakers = 9
We are assuming that a sound system consists of one of​ each .
Then by Fundamental principle of counting , we have
The number of different sound systems can he​ advertise = (Number of different CD​ players)x (Number of different receivers) x(Number of  different speakers)
= 6 x10 x 9 =540
Hence, the number of different sound systems can he​ advertise =540