Tough and Tricky questions: Probability.
Medical analysts predict that one over five of all people who are infected by a certain biological agent could be expected to be killed for each day that passes during which they have not received an antidote. What fraction of a group of 1,000 people could be expected to be killed if infected and not treated for three full days?
Choose one:
A) 16/81
B) 8/27
C) 2/3
D) 61/125
E) 65/81
At the end of each day we will have 4/5 alive. So after 3 days we will have (4/5)^3 people alive. Therefore, fraction of dead people will be 1-(4/5)^3=61/125.   The correct answer is 61/125.
<result>D</result>
Tough and Tricky questions: Probability.
Medical analysts predict that one over five of all people who are infected by a certain biological agent could be expected to be killed for each day that passes during which they have not received an antidote. What fraction of a group of 1,000 people could be expected to be killed if infected and not treated for three full days?