how to calculate mean from grouped data on graphical calculator?

does anyone know how to work out estimates of the mean and standard deviation from data that has midpoints, but more specifically on a graphical calculator? i have a standard casio fx-9750GII. i did this so long ago that i can't remember what to do. i've plugged in the midpoints into one column and the frequency into another, but when i calculate the mean from that its wrong! any help appreciated!

your method sounds correct... maybe you worked out the midpoints incorrectly ?

weird..i'm close to the answer but not close enough if i attach the question would you be able to tell me if i'm doing it right?

http://filestore.aqa.org.uk/subjects/AQA-MS-SS1B-W-QP-JAN11.PDF

its question 3, and i'm on part b. i got the midpoints as 0.96,0.99,1.02,1.05 etc etc basically adding 0.03 each time!

your midpoints look fine... have you checked that you entered the frequencies exactly ?

okay, and yeah i've checked. i get 1.065 as the mean but it says its 1.062 :P

it's definitely 1.062... the total of x*f is 106.2 not 106.5