Fifty fifth-grade students from each of four city schools were given a standardized fifth-grade reading test. After grading, each student was rated as satisfactory or not satisfactory in reading ability, with the following results:

School

1

2

3

4

Not satisfactory

7

10

13

6

Is there sufficient evidence to indicate that the percentage of fifth-grade students with an unsatisfactory reading ability varies from school to school? Use 1% level of significance level.

Solution:

H0 :p1=p2=p3=p4=p = 1/4

H1 : At least one proportion differs from at least one another.

I found df = 3, critical value = 11.3449, but I can't figure out how to find the observed value??

Expected value = np so E = 50*(1/4) = 12.5

Observed value??