B. 33.14
1) We need first to find the average between those classes. Since these data is a grouped data
50 - 59 Midpoint (Average) : (50+59)/2 = 54.5
40 -49 Midpoint (Average) : 44.5
30 - 39 Midpoint (Average) : 34.5
20 - 29 Midpoint (Average) : 24.5
10 - 19 Midpoint (Average):14.5
2) Now, we're going to write the formula of the Mean, placing those midpoints as the numerators and multiply by each frequency, and sum them all. On the Denominator, we'll place the frequencies. This way:
[tex]x\text{ =}\frac{54.5\cdot12+44.5\cdot25+34.5\cdot39+24.5\cdot32+14.5\cdot17}{12+25+39+32+17}=33.14[/tex]
So the mean of that distribution is 33.14, B
