122/400=0.305 compared with 0.4.
t=(0.305-0.4)/√(0.4×0.6/400)=-3.88 approx.
For significance level of 0.01 (2-tail test), critical value is 2.59.
The null hypothesis (that is, no significant difference from pp) is rejected, because the magnitude of 3.88 exceeds 2.59, so it is likely that pp is other than 0.4.