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The number of telephone calls made daily in a certain community between 8 P.M. and 9 P.M. has a mean of 352 and standard deviation of 31. What percentage of time will there be more than 400 telephone calls made in this community between 8 P.M. to 9 P.M.?

[Given that: P(0≤Z≤1.55)=0.4394P(0\leq Z\leq1.55)=0.4394, where ZZ is the standard normal variate]

Solution

✅ Correct Option: 3

Standardise: z=400−35231≈1.55z=\frac{400-352}{31}\approx1.55. Then P(Z>1.55)=0.5−0.4394=0.0606P(Z>1.55)=0.5-0.4394=0.0606, i.e. about 6.06% of the time.

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