Unit 7 Averages and range Sampling 8 Dan wants to select three students at random from Class 8W. There are 30 children in the class. Describe how he can make the choice fairly. 9 Communication Jo wants to find out people’s views on whether VAT should be charged for hairdressing. She asks a random sample of ten people at a shopping centre on a Monday morning for their views. Give two reasons why the results of her survey may not be reliable. Just guessing Feeling doubtful Confident What next? Use your results to decide whether to strengthen or extend your learning. Reflect 10 How sure are you of your answers? Were you mostly Challenge 11 This table gives information about the ages of members of a gym. Age Frequency, f 18–24 32 25– –40 Class mid-point, m 672 27 a b c d 1107 70 41–59 60–70 f×m 2650 14 Copy and complete the table to fill in the missing values. Work out an estimate of the mean age. Which class contains the median? Which is the modal class? Explain why this may be misleading. 7 Strengthen Averages and range 1 2 Lisa is training for a 200 m race. These are her latest times, in seconds, over that distance. 24, 25, 24, 24, 23, 24, 25, 23 a Copy and complete this sentence to predict the mean. I think Lisa’s mean time will be about ........................ b How many times are there? c Work out the total of all her times. d Work out Lisa’s mean time for the 200 m.. Here are the top ten midday temperatures, in °C, in Bridlington during October 2014. 16, 16, 16, 15, 14, 14, 14, 13, 12, 12 Work out the mean of these temperatures. Q1a hint The mean will be somewhere between the lowest value and the highest value. Your answer will be in seconds. Q1d hint total of times Mean = ______________ number of times Q2 hint Predict the mean first. How many temperatures are there? Check your answer °C with your prediction. Homework, practice and support: Foundation 7 Strengthen 199