Supplementary Exercise 8.1 of IPS7e
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The guideline for use of the normal approximation for the significance
test (or the "classical" z-test) is that n*p0>10 and n*(1-p0)>10, where 
p0 is the value being tested (slide 7L-12).

(a) no, because n*p0 = 10*0.4 = 4<10,

(b) yes, because both conditions are met: 100*0.6=60>10 and 100*0.4=40>10,

(c) no, because n*(1-p0) = 1000*0.004 = 4<10,

(d) yes, because both conditions are easily met.