Statistics - Esitmate Mean,Median,Standard deviation using Freq. table.

hello!

I am wondering if I could please get help with the below questions which are revision questions but I do not know how to do it.

Additional Problems: Grouped Data

1. Estimate the mean, median and the standard deviation of the following set of

grouped data that summarise the marks (out of 100) obtained in a statistics

exam for a sample of 150 computer science students.

Score...............Frequency

10- up to 20.........1

20- up to 30.........6

30- up to 40.........9

40- up to 50.........31

50- up to 60.........42

60- up to 70.........32

70- up to 80.........17

80- up to 90.........10

90- up to 100.........2

for the __mean__ do you calculate the fimi total and divide that by the total freq. ?

for the __median__ do you just divide the total freq. by 2 ? which gives us the m class

We can estimate the median by using L + j/f c

and for the standard deviation, I have no idea... ?

2. The gross hourly wages of a sample of 100 workers randomly selected from a

payroll list of a large company were tabulated as follows:

Hourly wages($)...................No: ofworkers

8- up to 10..................................11

10- up to 12................................17

12- up to 14................................32

14- up to 16................................27

16- up to 18................................13

Estimate the mean, median and the standard deviation of hourly wages for this

sample of workers

would be the same formula's as the previous question.