7 Problem-solving The probability of not being connected when ringing a customer support service is 30%. On a typical Monday, customers ring the service 400 times. How many of these calls would you expect to be connected? 8 An optician's records show that 21 of the last 50 customers bought designer frames and 14 of them bought two pairs of glasses. a Estimate the probability that the next customer orders i designer frames ii two pairs of glasses. b Of the next 200 customers, how many would you expect to order two pairs of glasses? Discussion Is the probability of a customer ordering designer 35 frames or two pairs of glasses 50? 9 Peter tested 10 batteries and found 80% lasted more than 30 hours. Sven tested 100 of the same batteries and found 90% lasted more than 30 hours. Whose results are more useful? 10 Problem-solving / Reasoning a Edward asked 20 people which charity they donate money to. 11 said Oxfam. Estimate the probability that a person donates money to Oxfam. b Odval asked 80 people which charity they donate money to. 45 said Oxfam. Use his data to estimate the probability that a person donates money to Oxfam. c Which estimate do you think is more reliable? Give a reason for your answer. d Edward and Odval shared their data. i Use their combined data to estimate the probability that a person donates money to Oxfam. Explore 11 Explore What is the probability that a drug will stop a headache? Is it easier to explore this question now you have completed the lesson? What further information do you need to be able to answer this? Reflect ii They interview another 200 people. How many would they expect to donate money to Oxfam? 12 Reflect Look back at the questions you answered in this lesson. a Make a list of all the different maths skills you have used. b Was there a question you found particularly difficult? What made it difficult? c Was there a question you found easy? 181 Delta 2, Section 8.3 Key point The more data you have, the more confident you can be about any conclusions based on the data.