a.
P(60<X<70)=P(X<70)−P(X≤60)
=P(Z<570−56)−P(Z≤560−56)
=P(Z<2.8)−P(Z≤0.8)
≈0.9974449−0.7881446≈0.209300
0.209300(800)=167 167 students weigh between 60 kg and 70 kg.
b.
P(X>68)=1−P(X≤68)
=1−P(Z≤568−56)=1−P(Z≤2.6)
≈0.004661
0.004661(800)=4 4 students weigh more than 68 kg.
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