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Example 5 - Chapter 15 Class 9 Probability (Term 2)

Last updated at Aug. 25, 2021 by

Example 5 - The record of a weather station shows that - Examples

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Example 5 - Chapter 15 Class 9 Probability - Part 2

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Example 5 - Chapter 15 Class 9 Probability - Part 3

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Transcript

Example 5 The record of a weather station shows that out of the past 250 consecutive days, its weather forecasts were correct 175 times. (i) What is the probability that on a given day it was correct? The total number of days for which the record is available = 250 Number of days when forecast was correct = 175 P(the forecast was correct on a given day) = (π‘π‘’π‘šπ‘π‘’π‘Ÿ π‘œπ‘“ π‘‘π‘Žπ‘¦π‘  π‘“π‘œπ‘Ÿ π‘€β„Žπ‘’π‘› π‘“π‘œπ‘Ÿπ‘’π‘π‘Žπ‘ π‘‘ π‘€π‘Žπ‘  π‘π‘œπ‘Ÿπ‘Ÿπ‘’π‘π‘‘)/(π‘‡π‘œπ‘‘π‘Žπ‘™ π‘›π‘’π‘šπ‘π‘’π‘Ÿ π‘œπ‘“ π‘‘π‘Žπ‘¦π‘  π‘“π‘œπ‘Ÿ π‘€β„Žπ‘–π‘β„Ž π‘‘β„Žπ‘’ π‘Ÿπ‘’π‘π‘œπ‘Ÿπ‘‘ 𝑖𝑠 π‘Žπ‘£π‘Žπ‘–π‘™π‘Žπ‘π‘™π‘’) = 175/250 = 0.7 Example 5 (Method 1) The record of a weather station shows that out of the past 250 consecutive days, its weather forecasts were correct 175 times. (ii) What is the probability that it was not correct on a given day? The total number of days for which the record is available = 250 The number of days when the forecast was not correct = 250 – 175 = 75 P(the forecast was not correct on a given day) = (π‘π‘’π‘šπ‘π‘’π‘Ÿ π‘œπ‘“ π‘‘π‘Žπ‘¦π‘  π‘“π‘œπ‘Ÿ π‘€β„Žπ‘’π‘› π‘“π‘œπ‘Ÿπ‘’π‘π‘Žπ‘ π‘‘ π‘€π‘Žπ‘  π‘›π‘œπ‘‘ π‘π‘œπ‘Ÿπ‘Ÿπ‘’π‘π‘‘)/(π‘‡π‘œπ‘‘π‘Žπ‘™ π‘›π‘’π‘šπ‘π‘’π‘Ÿ π‘œπ‘“ π‘‘π‘Žπ‘¦π‘  π‘“π‘œπ‘Ÿ π‘€β„Žπ‘–π‘β„Ž π‘‘β„Žπ‘’ π‘Ÿπ‘’π‘π‘œπ‘Ÿπ‘‘ 𝑖𝑠 π‘Žπ‘£π‘Žπ‘–π‘™π‘Žπ‘π‘™π‘’) = 75/250 = 0.3 Example 5 (Method 2) The record of a weather station shows that out of the past 250 consecutive days, its weather forecasts were correct 175 times. (ii) What is the probability that it was not correct on a given day? P(the forecast was not correct on a given day) = 1 – P(forecast was correct on a given day) = 1 – 0.7 = 0.3

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Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 12 years. He provides courses for Maths and Science at Teachoo.