2006 doubts

[Arushi :))]

c 135/ 256
d 131/ 256

[Dreyfus]

The possible cases can be:
Case1 : when both the patients gets infected on day 1
Case2 : when exactly 1 of them gets infected on day 1 so that other patient will get infected on day 2 with certainty
Case3: when none of the patient catches infection on day 1 nd simultaneously gets infected on day 2
Pr(case 1) = 1/16
Pr(case 2) = 6/16
PR(case3) = 9/256
Pr ( both patients have contracted the infection by the end of day 2) = 1/16 + 9/16 +9/256 = 121/256

[hbk]

q 47 it will have 3 cases
both got on 1st day 1/4 × 1/4
both got in 2nd day 3/4×1/4 ×3/4×1/4
one of them got it on 1st day 2(3/4×1/4)
Add all 3 cases u will get 121/256
and for ques 47 i m also confse b/w b or c but amit sir has given d

[Sumit Goel]

Amit Sir has also given (b).
Check this: http://economicsentrance.weebly.com/uploads/1/1/0/5/1105777/dse2006_ans.pdf