There are seven pairs of black shoes and 5 pairs of white shoes .Tey all are put into a box and shoes are drawn at a time.To ensure that at leat one pair of black shoes are taken out,what is the number of shoes required to be drawn out.
a. 12
b. 13
c. 7
d. 18

What is the minimum number of shoes required to be drawn out so as to get at leat 1 pair of correct shoes.
a. 12
b. 7
c. 13
d. 18

• 1st Ques:
  Answer is d. 18
  
  White shoes: 5*2=10
  Black shoes: 7*2=14
  Total shoes: 14+10=24
  
  Now, for the worst case,
  1st- All the white shoes are taken out, so 10 shoes are drawn.
  2nd- All the one sided (assume only left side) black shoes are drawn. So, another 7 shoes are drawn.
  So, in the box left shoes are= 24-17=7
  Those 7 shoes are right sided black shoes.
  
  So on the 18th draw we'll get the 1st right footed black shoe, i.e. the 1st pair of black shoe.
  
  So, the no. of shoes required to be drawn out is: 18 (Ans).
• 8 years agoHelpfull: Yes(49) No(0)
• 2nd Ques:
  Answer is c. 13
  
  For worst case:
  All the one sided (assume only left) white shoes, total draws required: 5
  All the one sided (assume only left) black shoes, total draws required: 7
  So, total draws are: 5+7=12
  Next draw or 13th draw will contain any color right footed shoe, i.e. making at least one correct pair.
  So, minimum number of shoes required to be drawn out is: 13 (Ans).
• 8 years agoHelpfull: Yes(34) No(2)
• answer for 1st part is 18. 24 - 7 +1.
  answer for 2nd part is 13. There are 24 objects. (24/2)+1
• 8 years agoHelpfull: Yes(0) No(3)