Random sampling question?

Xbar( Math ) = (68+83+72+55+92)/5 = 74
Xbar( English ) = 74.6
Xbar( Physics ) = 75.8
Xbar( Chemistry ) = 71.8
Total_Xbar = ( 74*5 + 74.6*5 + 75.8*5 + 71.8*5 )/20 = 74.05

SST
= Σ Σ ( X ij - Toral_Xbar )^2
= (68-74.05)^2 + (83-74.05)^2 + ..... + (66-74.05)^2 + (87-74.05)^2
= 2772.95

SS_Courses
= 5 * [ (74-74.05)^2 + (74.6-74.05)^2 + (75.8-74.05)^2 + (71.8-74.05)^2 ]
= 42.15

ANOVA :
SSE = SST - SS_Courses = 2772.95 - 42.15 = 2730.8
df_Courses = 4 - 1 = 3
df_Total = 4*5 - 1 = 19
df_Error = 19 - 3 = 16
V_Courses = SS_Courses / df_Courses = 42.15 / 3 = 14.05
V_Error = SSE / df_Error = 2730.8 / 16 = 170.675
F 0.05 ( 3 , 16 ) = 3.24
F0 = V_Courses / V_Error = 14.05 / 170.675 = 0.082 < 3.24

Hence,
the courses are "not" of unequal difficulties. ..... Ans