Example 7 - Chapter 14 Class 10 Probability

Transcript

Example 7 (i) 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) = (𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐𝑎𝑟𝑑𝑠 𝑤𝑖𝑡ℎ 𝑛𝑎𝑚𝑒 𝑜𝑓 𝑎 𝑔𝑖𝑟𝑙)/(𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐𝑎𝑟𝑑𝑠) = 25/40 = 𝟓/𝟖 Example 7 (ii) (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) = (𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐𝑎𝑟𝑑𝑠 𝑤𝑖𝑡ℎ 𝑛𝑎𝑚𝑒 𝑜𝑓 𝑎 𝑏𝑜𝑦)/(𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐𝑎𝑟𝑑𝑠) = 15/40 = 𝟑/𝟖 Example 7 (ii) (Method 2) There are 40 students in Class X of a school of whom 25 are girls & 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