turtle turtle Posted March 26, 2016 Report Share Posted March 26, 2016 Hi, the question is: 5% of computer processors are defective. Processors are selected at random and put into packs of 15. (b) Two packets are selected at random. Find the probability that there are at least two defective processors in either packet please help, thanks so much!! Reply Link to post Share on other sites More sharing options...
kw0573 Posted March 26, 2016 Report Share Posted March 26, 2016 (edited) @turtle turtle X ~ B(15, 0.05), where X is number of defects First find probability that a single packet has at least two defects. P(X >= 2) = 1 - P(X=0) - P(X=1) = 1 - (0.95)15 - 15(0.95)14(0.05) = 0.17095 then make a new distribution for SUCH packets Y ~ B(2, 0.17095), where Y is the number of Packets. A Packet is a packet with at least two defective processors. I am not too sure what "either packet" means. It can mean exactly one packet, at least one packet, or two packets. Respectively, you would find P(Y = 1), P(Y >= 1), or P(Y = 2) depending on the correct interpretation of the problem. Edited March 26, 2016 by kw0573 1 Reply Link to post Share on other sites More sharing options...
turtle turtle Posted March 26, 2016 Author Report Share Posted March 26, 2016 4 hours ago, kw0573 said: @turtle turtle X ~ B(15, 0.05), where X is number of defects First find probability that a single packet has at least two defects. P(X >= 2) = 1 - P(X=0) - P(X=1) = 1 - (0.95)15 - 15(0.95)14(0.05) = 0.17095 then make a new distribution for SUCH packets Y ~ B(2, 0.17095), where Y is the number of Packets. A Packet is a packet with at least two defective processors. I am not too sure what "either packet" means. It can mean exactly one packet, at least one packet, or two packets. Respectively, you would find P(Y = 1), P(Y >= 1), or P(Y = 2) depending on the correct interpretation of the problem. Hi thanks so much for the reply!! Yeah, I was really confused about the word 'either' and after looking at the answer (0.0292) you're right, it means that both of them have to be greater than/equal to 2. Is it always the case that either means both, because it's really ambiguous? ty again Reply Link to post Share on other sites More sharing options...
kw0573 Posted March 26, 2016 Report Share Posted March 26, 2016 3 hours ago, turtle turtle said: Hi thanks so much for the reply!! Yeah, I was really confused about the word 'either' and after looking at the answer (0.0292) you're right, it means that both of them have to be greater than/equal to 2. Is it always the case that either means both, because it's really ambiguous? ty again In my experience IB has typically been quite clear in these directions in math, especially because it can lead to different answers. 1 Reply Link to post Share on other sites More sharing options...
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