Average Study Hours Calculation

A recent survey was conducted to find the number of hours students spent on studying each week. The survey results showed the following distribution of study hours:

• 0-5 hours: 30 students
• 6-10 hours: 25 students
• 11-15 hours: 20 students
• 16-20 hours: 15 students
• More than 20 hours: 10 students

What is the average number of hours spent studying per week by the surveyed students?