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Last updated at May 29, 2018 by Teachoo

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Example 7 There are 40 students in Class X of a school of whom 25 are girls and 15 are boys. The class teacher has to select one student as a class representative. She writes the name of each student on a separate card, the cards being identical. Then she puts cards in a bag and stirs them thoroughly. She then draws one card from the bag. What is the probability that the name written on the card is the name of a girl? Total number of cards = Total number of students = 40 Number of cards with the name of a girl = Number of girls = 25 P (card with name of a girl) = ( )/( ) = 25/40 = 5/8 Example 7(Method 1) There are 40 students in Class X of a school of whom 25 are girls and 15 are boys. The class teacher has to select one student as a class representative. She writes the name of each student on a separate card, the cards being identical. Then she puts cards in a bag and stirs them thoroughly. She then draws one card from the bag. What is the probability that the name written on the card is the name of (ii) a boy? Total number of cards = Total number of students = 40 Number of cards with the name of a boy = Number of boy = 15 P (card with name of a boy) = ( )/( ) = 15/40 = 3/8 Example 7(Method 2) There are 40 students in Class X of a school of whom 25 are girls and 15 are boys. The class teacher has to select one student as a class representative. She writes the name of each student on a separate card, the cards being identical. Then she puts cards in a bag and stirs them thoroughly. She then draws one card from the bag. What is the probability that the name written on the card is the name of (ii) a boy? The card chosen can be of a boy or a girl P(card with name of a boy) = 1 P(Card with not the name of a boy) = 1 P(card with name of the girl) = 1 5/8 = 3/8

About the Author

Davneet Singh

Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 9 years. He provides courses for Maths and Science at Teachoo.