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General Mathematics Paper 2, Nov/Dec. 2009  
Questions: 1 2 3 4 5 6 7 8 9 10 11 12 13 Main
General Comments
Weakness/Remedies
Strength
Question 3

The probability that a malaria patient (M) survives when administered with a newly discovered drug is 0.27 and the probability that a thyphoid patient (T) survives when injected with another newly discovered drug is 0.85.  What is the probability that

  • either of the two patients survives?
  • neither of two patients survive?
  • at least one of the two patients survive?

           
Give your answers correct to 2 significant figures.

_____________________________________________________________________________________________________
Observation

It was reported that the performance of candidates in this question was not commendable.  They found it difficult; hence they scored very low marks.  They were expected to show that if P(M) = probability of the malaria patient surviving = 0.27, probability of not surviving, P(M¢) = 1- 0.27 = 0.73.  Similarly, if P(T) = probability of the thypoid patient surviving = 0.85, then probability of not surviving = P(T1)  =  1-P(T) = 1- 0.85 = 0.15.  Probability of either surviving = (0.27 x 0.15) + (0.85 x 0.73) = 0.66. Probability of neither surviving =

(0.73 x 0.15) = 0.11.  Probability of at least one surviving = 1- 0.11 = 0.89.
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