The claim is that the proportion of peas with yellow pods is

The claim is that the proportion of peas with yellow pods is equal to 0.25 (or 25%). The sample statistics from one experiment include 420 peas with 117 of them having yellow pods. Find the value of the test statistic.

Solution

Formulating the null and alternatuve hypotheses,          
          
Ho:   p   =   0.25
Ha:   p   =/=   0.25

As we see, the hypothesized po =   0.25      

Getting the point estimate of p, p^,          
          
p^ = x / n =    0.195238095      
          
Getting the standard error of p^, sp,          
          
sp = sqrt[po (1 - po)/n] =    0.021128856      
          
Getting the z statistic,          
          
z = (p^ - po)/sp =    -2.591806381   [answer]