GATE CSE
First time here? Checkout the FAQ!
x
+2 votes
160 views

A box contain 10 screws out of which 3 are defective.If two screws are drawn at random WITH REPLACEMENT.What is the probability that no screw is defective?

Answer given as 7c2/10C2

my question is ,as its given With Replacement. So why not it is (7/10)*(7/10)

asked in Combinatory by Veteran (18.5k points)  
edited by | 160 views
@uddipto.. i guess in your ques. , the point is that we are taking 2 screws simultaneously not one by one.if it has been one by one then the one which we had taken earlier can be put into bag again but when you are taking 2 screws simultaneously then with replacement won't come into picture. it is like when you are taking only 1 object from bucket, in that case it does not matter that it is with or without replacement.not quite sure if ques is answered using this logic or not!
i was wrong! it should be 7/10 * 7/10. you are correct @uddipto
No problem! even i was confused by the answer! testbook massacre

2 Answers

+5 votes
Best answer

......................

answered by Veteran (48.5k points)  
selected by
why does this formula fail (n+r-1)C2 i.e 8C2/11C2 ? since with replacement
+3 votes

See here the key thing is :

a) The population which is a box of  10 screws and hence finite .

b) Screws are drawn with replacement.

So the assumption of binomial distribution will hold..

So P ( no defective ) = 2C0 (7/10)2

                               = 0.49

Hence 0.49 is correct answer.. 

answered by Veteran (66.5k points)  
habib i did the same.. But testbook made it incorrect
Dont worry..Ur concept is correct..

Related questions

0 votes
0 answers
1
asked ago in Combinatory by Vasu Srivastava (37 points)   | 37 views


Top Users Jun 2017
  1. Bikram

    3704 Points

  2. Arnab Bhadra

    1502 Points

  3. Hemant Parihar

    1502 Points

  4. Niraj Singh 2

    1481 Points

  5. junaid ahmad

    1432 Points

  6. Debashish Deka

    1384 Points

  7. Rupendra Choudhary

    1220 Points

  8. rahul sharma 5

    1220 Points

  9. Arjun

    1158 Points

  10. srestha

    1006 Points

Monthly Topper: Rs. 500 gift card
Top Users 2017 Jun 26 - Jul 02
  1. Arjun

    198 Points

  2. akankshadewangan24

    152 Points

  3. Debashish Deka

    138 Points

  4. Hira Thakur

    130 Points

  5. Soumya29

    104 Points


23,399 questions
30,111 answers
67,489 comments
28,424 users