Sandeep A. answered • 12/19/12

Biostatistician / Statistician

You have 4 cells with frequescise in your problem -

95 , 25, 105 , 275

best way to do this problem is make 2X2 table and put observed and expected frequencies in the table.

as explained above to calculate expected frequency you will take row total & column total & devide by grand total for each cell.

so for 95 - Exp freq = (120*200/500) = 48

for 25 - Exp freq = ( 120*300/500) = 72

for 105 Exp Freq = ( 380*200/500) = 152

for 275 Exp Freq = ( 275*300/500) = 228

Now calculate this for each cell (Observed - Expected) ^2/ Expected and add them -

( 95-48)^2/48 + (25-72)^2/72 + ( 105-152)^2/152 + ( 275-228)^2/ 228 = 46.02 + 30.68 + 14.53 + 0.69 = 100.9

degrees of freedom = (# of rows -1 ) ( # of columns-1) = ( 2-1)(2-1) = 1

let me know if you have any questions or you don't understand anything.