Math Help - cumulative freqency

1. cumulative freqency

for eg. the length of 30 nails were measured. their lengths are represented in a table with for eg. 0 to 4 cm ,frequency of 14. the qn asked me to draw a histogram and then find the mean length of the nails.i dont know how to determine the mean length. what should i do?

2. Originally Posted by helloying
for eg. the length of 30 nails were measured. their lengths are represented in a table with for eg. 0 to 4 cm ,frequency of 14. the qn asked me to draw a histogram and then find the mean length of the nails.i dont know how to determine the mean length. what should i do?

Mean $=\frac{\sum fx}{\sum f}$

Take midpoints of every class for x .