"a)\\xi\\text{ is a random variable: the duration a customer spends in the shop}.\\\\\n\\xi \\in N(140; 18^2).\\\\\nP\\{\\xi>180\\}=1-P\\{\\xi\\leq 180\\}=1-F(180)=1-\\Phi(\\frac{180-140}{18})\\approx\\\\\n\\approx 1-0.9869=0.0131.\\\\\nF(x)=\\frac{1}{\\sqrt{2\\pi}18}\\int_{-\\infty}^x e^{-\\frac{(z-140)^2}{2\\cdot 18^2}}dz\\\\\n\\Phi(x)=\\frac{1}{\\sqrt{2\\pi}}\\int_{-\\infty}^x e^{-\\frac{z^2}{2}}dz\\\\\nb) P\\{\\xi\\leq t\\}=F(t)=\\Phi(\\frac{t-140}{18})=0.15\\\\\n\\frac{t-140}{18}\\approx -1.04\\\\\nt\\approx 121.28\\approx 122.\\\\\n\u0441) \\text{Average of the amount of money equals } 100+80(1.1)=\\\\\n=188 (140=60+80).\\\\\n\\text{Median equals average because the duration a customer}\\\\\n\\text{spends in the shop follows a normal distribution with mean 140 minutes}\\\\\n\\text{and standard deviation 18 minutes}.\\\\\n\\text{Standard deviation of the amount of money equals } 18(1.1)=19.8.\\\\\nd) 3\\text{ hours}=60+2\\cdot 60.\\\\\n\\text{A customer needs to pay } 100+120(1.1)=232.\\\\\ne)\\text{In b) } t\\approx 122.\\\\\nk=100+62(1.1)=168.2.\\\\\nf)\\text{Spending of a customer in \u201cFunBakery\u201d has normal distribution}\\\\\n\\text{with mean 188 and standard deviation 19.8. Median of the amount}\\\\\n\\text{of money equals mean}."
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