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Calculate the mean of the following data :

 Class  \(4-7\) \(8 -11\) \(12-15\) \(16-19\) 
 Frequency  \(5\)  \(4\)  \(9\) \(10\) 
 
Answer:  
 
The mean is .
 
[Note: Enter the answer in to two decimal number.]