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3 marksBasic Laws of Probability

CSEC Additional Mathematics · 2018 · Paper 2 · Question 7(b)(ii)

Insecticides A, B or C are applied on lots Q, R and S. The same crop is planted on each lot and the lots are of the same size. The probability that a group of farmers will select A, B or C is 40%, 25% and 35% respectively. The probability that insecticide A is successful is 0.8, that B is successful is 0.65, and that C is successful is 0.95.

An insecticide is selected at random, determine the probability that it is unsuccessful.

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Other parts of this question

  1. 7(a)(i)Determine the median score.[2 marks]
  2. 7(a)(ii)Calculate the interquartile range of the scores.[3 marks]
  3. 7(a)(iii)In the space below, construct a box-and-whisker plot to illustrate the data and comment on the shape of the distribution.[4 marks]
  4. 7(b)(i)Illustrate this information on a tree diagram showing ALL the probabilities on ALL branches.[3 marks]
  5. 7(c)(i)Calculate the probability of obtaining a 5 on the 2nd toss, given that a 5 was obtained on the 1st toss.[2 marks]
  6. 7(c)(ii)Determine the probability that a 5 is obtained on both tosses.[2 marks]
  7. 7(c)(iii)Explain why the answers in (c) (i) and (c) (ii) are different.[1 mark]

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