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Q.Define outcomes and sample space. The numbers 1, 2, 3 and 4 are written separately on four slips of paper. The slips are put in a box and mixed thoroughly. A person draws two slips from the box, one after the other, without replacement. Describe the sample space for the experiment. (1+1+4=6) OR Two dice are thrown and the sum of the numbers which come up on the dice is noted. Consider the following events associated with this experiment: A: 'the sum is even'; B: 'the sum is a multiple of 3'; C: 'the sum is less than 4'; D: 'the sum is greater than 11'. Which pairs of these events are mutually exclusive?

Assam AhsecAHSEC Higher Secondary (HS) 1st Year Examination 2020Subjective· 6mImportance★★★★★
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Since the two slips are drawn one after another without replacement, order matters and repeats are impossible, giving 12 ordered-pair outcomes.

Definitions. An outcome is a single possible result of a random experiment (e.g. drawing the slip marked '2' first). The sample space, denoted SS, is the SET of ALL possible outcomes of the experiment.

Main question. Four slips numbered 1,2,3,41,2,3,4 are in a box. A person draws two slips one after another, WITHOUT replacement. We must describe the sample space.

Since the draws happen in sequence (one after another) and are without replacement:

  • The first draw can be any of the 4 numbers.
  • The second draw can be any of the remaining 3 numbers (it cannot repeat the first).
  • Order matters, since 'draw 1 then 2' is a different outcome from 'draw 2 then 1' (they are distinguishable draws).

So each outcome is an ordered pair (a,b)(a,b) with a≠ba\ne b, both from {1,2,3,4}\{1,2,3,4\}. The full sample space (all 4×3=124\times3=12 such pairs) is:

S={(1,2),(1,3),(1,4),(2,1),(2,3),(2,4),(3,1),(3,2),(3,4),(4,1),(4,2),(4,3)}S=\{(1,2),(1,3),(1,4),(2,1),(2,3),(2,4),(3,1),(3,2),(3,4),(4,1),(4,2),(4,3)\}


OR alternative. Two dice are thrown; the sum of the numbers shown is noted. Consider the events (sums range from 2 to 12):

  • AA: 'the sum is even' ={2,4,6,8,10,12}=\{2,4,6,8,10,12\}
  • BB: 'the sum is a multiple of 3' ={3,6,9,12}=\{3,6,9,12\}
  • CC: 'the sum is less than 4' ={2,3}=\{2,3\}
  • DD: 'the sum is greater than 11' ={12}=\{12\} …

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