1. x & y stand in a line with 6 other people.what is the probability that there are 3 persons between them ? ans is 1/7,how?
2. four digits 1,2,4 & 6 are selected at random to form a four digit number.what is the probability that the number so formed,would be divisible by 4? ans is 1/3,how?
3. a packet of 10 electronic components is known to include 3 defectives.if 4 components are selected from the packet at random,what is the expected value of the number of defective? ans is 1.20,how?
1. Let us write down all the possibilities: In all there are 8 persons. Let us put X at top position and Y at 5 th position. Similarly, take X to 2,3,4 positions. We can reverse these positions also. Thus there are 8 possibilities. In all X and Y have 8*7 possibilities,
so 8 /56 is the answer. and it is 1/7.....
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