I am taking CIE statistics 1 this year.
I have doubts relating to mean,median and mode. Although they are just the basics, i am still confused:
1) whenever we draw a histogram, do we always have to take 'frequency densities' on the y-axis? Or do we also take 'frequency' on the y-axis?
2) for grouped data, and the frequencies given, how do we find the median without drawing the cummulative frequency graph?
3) for grouped data, and frequencies given, how do we find the upper quartile and lower quartile?
4) what is the difference between variance and standard deviation?
Thanks.