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In a study about a pandemic, data of 900900 persons was collected. It was found that 190190 persons had symptom of fever, 220220 persons had symptom of cough, 220220 persons had symptom of breathing problem, 330330 persons had symptom of fever or cough or both, 350350 persons had symptom of cough or breathing problem or both, 340340 persons had symptom of fever or breathing problem or both, 3030 persons had all three symptoms (fever, cough and breathing problem). If a person is chosen randomly from these 900900 persons, then the probability that the person has at most one symptom is.

Full solution

Q. In a study about a pandemic, data of 900900 persons was collected. It was found that 190190 persons had symptom of fever, 220220 persons had symptom of cough, 220220 persons had symptom of breathing problem, 330330 persons had symptom of fever or cough or both, 350350 persons had symptom of cough or breathing problem or both, 340340 persons had symptom of fever or breathing problem or both, 3030 persons had all three symptoms (fever, cough and breathing problem). If a person is chosen randomly from these 900900 persons, then the probability that the person has at most one symptom is.
  1. Calculate Fever Only: Calculate the number of people with exactly one symptom. We use the inclusion-exclusion principle:\newline- Only fever: 190(330220)(340220)+30=40190 - (330 - 220) - (340 - 220) + 30 = 40\newline- Only cough: 220(330190)(350220)+30=40220 - (330 - 190) - (350 - 220) + 30 = 40\newline- Only breathing problem: 220(350220)(340190)+30=40220 - (350 - 220) - (340 - 190) + 30 = 40
  2. Calculate Cough Only: Add the number of people with exactly one symptom to find the total number of people with at most one symptom: 4040 (only fever) + 4040 (only cough) + 4040 (only breathing problem) = 120120

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