91Ó°ÊÓ

Two surveys are conducted to measure the effect of an advertising campaign for a certain brand of detergent. 7 In the first survey, interviewers ask house- wives whether they use that brand of detergent. In the second, the interviewers ask to see what detergent is being used. Would you expect the two surveys to reach similar conclusions? Give your reasons.

A sorcerer has hidden a Porsche in one of an infinite row of boxes The sorcerer will let you drive away with the car if you can find it. But you are only allowed to look in 11 boxes. He agrees to give you a hint, by tossing a coin 100 times and counting the number of heads. He will not tell you this number, or the number of the box in which he hid the car. But he will tell you the sum of the two numbers. $$ \begin{array}{l}{\text { (a) If the sum is } 65, \text { which } 11 \text { boxes would you look in? }} \\ {\text { (b) As in (a), except replace } 65 \text { by } 95 \text { . }} \\ {\text { (c) What is the general rule? }} \\\ {\text { (d) Following this rule, how likely are you to get the Porsche? }}\end{array} $$