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Question: Answered & Verified by Expert
Let X be a set containing 10 elements and PX be its power set. If A and B are picked up at random from PX, with replacement, then the probability that A and B have equal number of elements is:
MathematicsProbabilityJEE MainJEE Main 2015 (10 Apr Online)
Options:
  • A 210-1220
  • B 20C10220
  • C 20C10210
  • D 210-1210
Solution:
2093 Upvotes Verified Answer
The correct answer is: 20C10220

The power set of X will contain 210 elements where each element is subset of A in which 
10C0 will contain 0  element.
10C1 will contain 1 element.
10C2 will contain 2 elements.



10C10     will contain 10 elements.
So total numbers of ways in which we can select two sets with replacement is 
And favorable cases would be 10C010C0+10C1.10C1+ +10C10.10C10=20C10
Hence, Probability would be  = 20C10220
 

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