[!TLDR] Use class midpoints as $x_i$; weighted mean then $\frac1N\sum f_i|x_i-\bar x|$. [!ANSWER] Mean $=35$ …

The class midpoints are $x_i:15,25,35,45,55$ with frequencies $f_i:5,10,20,10,5$, so $N=5+10+20+10+5=50$. Now $\sum f_ix_i=15(5)+25(10)+35(20)+45(10)+55(5)=75+250+700+450+275=1750$, giving $\bar x=1750/50=35$. Absolute deviations $|x_i-35|$: $20,10,0,10,20$. Weighted: $f_i|x_i-\bar x|=5(20)+10(10)+20(0)+10(10)+5(20) …

Find the class midpoints, the frequency-weighted mean, then weight each absolute deviation b …

Using the class width or a class limit in place of the midpoint $x_i=\frac{\text{lower}+\text{u …