Suppose that 20% of a herd of cows is infected with a particular disease. (a) What is the probability that the first diseased cow is the 3rd cow tested?
(b) What is the probability that 4 or more cows would need to be tested until a diseased cow?

Best answer that i found on yahoo ok   set :   x= length of 2nd piece in cm  x- 3= length of 1st piece in cm  x-4= length of 3rd piece in cm  then since you know they all came from the 20 cm ribbon you add them together and set them equal to 20x+ x-3 +x-4 = 20  3x - 7= 20  3x= 27  x= 9  the shortest piece is the third piece which is x- 4  x-4  9-4 = 5  the length of the smallest piece is 5 cm.  the other lengths are  9 cm  6 cm

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