Question

Internet providers: In a survey of 780 homeowners with high-speed Internet, the average monthly cost of a high-speed Internet plan was $64.22 with standard deviation S10.75. Assume the plan costs to be approximately bell-shaped. Estimate the number of plans that cost between $42.72 and $85.72. pprosimately bell-shaped. The number of plans that cost between $42.72 and $85.72 is

Answer 1

given that: n = 780 Let x be plan costs X ~ N (64.22, (10.75)^2) mu = 64.22 sigma = 10.75 p[42.72 < x < 85.72] = p[42.72 - 64.22/10.75 < x - mu/sigma < 85.72 - 64.22/10.75] = p[-2 < z < 2] = p[z < 2] - p[z < - 2] using z - table we get = 0.977 - 0.023 = 0.954 Hence The number of plans = n times p = 0.954 times 780 = 744.12 The number of plans = 744.12