Solution
We take the mid-value of each interval for the calculation of mean of the given distribution.
$$\therefore\ $$Mean = $$\frac{\left(15\times5\right)+\left(25\times10\right)+\left(35\times7\right)+\left(45\times8\right)}{5+10+7+8}=\frac{930}{30}=31$$
Hence, the correct answer is Option B
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