The ideas and steps to solve the problem are as follows:
First, calculate the total class size: 16÷2/5=40.
Then calculate the percentage of each group in the class:
Calligraphy group: 9÷40× 100%=22.5%
Art group: 4÷40× 100%= 10%
Music group: 5÷40× 100%= 12.5%
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