The GPA for a class of ten females and seven males are recorded. The mean GPA of females is 3.07 and the standard deviation is 0.53. The mean GPA for males is also 3.07 and the standard deviation is 0.68. What is standard the deviation for all students ?

Attempt to solution:

Girls

$\displaystyle 0.53=\frac{{xi-3.07}^2}{9}$

$\displaystyle xi=5.2541$ or $\displaystyle 0.8859$

$\displaystyle 0.68=\frac{{xi-3.07}^2}{6}$

Boys

$\displaystyle

xi=5.0899$ or $\displaystyle xi=1.051$

Guys l am stuck here. It seems like l am in a vicious cycle. What should l do ?