The mean of the following distribution is Class $0-5$ $5-10$ $10-15$ $15-20$ $20-25$ $25-30$ Frequency $4$ $5$ $7$ $12$ $7$ $5$

Using the step deviation method, the class mark h is 5 and we take the assumed mean a as 17.5. The deviations multiplied by frequencies give a total of negative 10. The total frequency is 4 plus 5 plus 7 plus 12 plus 7 plus 5, which equals 40. The mean is 17.5 plus (negative 10 divided by 40) times 5, which equals 17.5 minus 1.25, resulting in 16.

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