A chip manufacturer makes defective chips with probability 0

A chip manufacturer makes defective chips with probability 0.1 and non-defective chips with probability 0.9. Assume that chips are independent

(3)mean=n*p=1000*0.1=100

standard deviation =sqrt(n*p*(1-p))

=sqrt(1000*0.1*0.9)

=9.486833

So the probability is

P(X>50) = P((X-mean)/s >(50-100)/9.486833)

=P(Z>-5.27) = 0.9999 (from standard normal table)

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(4) P(50<X<150)

=P((50-100)/9.486833<Z<(150-100)/9.486833)

=P(-5.27<Z<5.27)

=0.9999 (from standard normal table)