Latest TCS Aptitude Question SOLUTION: A drawer holds 4 red hats and 4 blue hats. What is the probability of getting exactly three red hats or exactly 3 blue hats while taking out 4 hats randomly out of the drawer and i

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A drawer holds 4 red hats and 4 blue hats. What is the probability of getting exactly three red hats or exactly 3 blue hats while taking out 4 hats randomly out of the drawer and immediately returning every hat to the drawer before taking out the next?
option
A. 1/2
B. 1/8
C. 1/4
D. None of these

Asked In TCS max (10 years ago)

Unsolved Read Solution (6)

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Read Solution (6) :

Arindam Dhara  (10 years ago)

possible ways
one red (1/2) and 3 blue(1/2 * 1/2 *1/2)= 1/16
one blue (1/2) 3 red (1/2 * 1/2 *1/2)= 1/16.

so 'or'ing two conditions we get = 1/16 + 1/16 = 1/8 ans B

Is this solution Helpfull? Yes (22) | No (12)  

chaitanya  (10 years ago)

1/2

p(drawing a red hat) = p(drawing a blue hat) = 4/8 = 1/2

exactly 3 R in 4 draw:
4 ways
BRRR
RBRR
RRBR
RRRB

each of these have prob : 1/2 * 1/2 * 1/2 * 1/2 = 1/16

thus p(drawing exactly 3 R hats) = 4 * 1/ 16 = 1/4

similarly, p(drawing exactly 3B hats) = 1/4

p(3 R or 3 B) = 1/4 + 1/4 = 1/2

Is this solution Helpfull? Yes (22) | No (3)  

shivangi  (10 years ago)

we also have to see the arrangement
like RRRB+RBRR+RRBR+BRRR
SIMILARLY FOR THE SECONDCASE OF BLUE
So robability shud b
4/16+4/16=1/2

Is this solution Helpfull? Yes (6) | No (6)  

Nitin Kumar  (10 years ago)

answer c.
1/4

Is this solution Helpfull? Yes (5) | No (9)  

Divyang Agarwal  (10 years ago)

probability of getting 1 red =4/8=1/2
After replacement, again the probability of getting red is 1/2.

probability for exactly 3 red=1/2*1/2*1/2=1/8
Similarly probability for getting 3 blue after each replacement is also 1/8
Total probability=1/8+1/8=1/4 Ans

Is this solution Helpfull? Yes (2) | No (9)  

Shashank Salaj  (10 years ago)

1/2(ans)

p(drawing a red hat) = p(drawing a blue hat) = 4/8 = 1/2

exactly 3 R in 4 draw:
4 ways
BRRR
RBRR
RRBR
RRRB

each of these have prob : 1/2 * 1/2 * 1/2 * 1/2 = 1/16

thus p(drawing exactly 3 R hats) = 4 * 1/ 16 = 1/4

similarly, p(drawing exactly 3B hats) = 1/4

p(3 R or 3 B) = 1/4 + 1/4 = 1/2

Is this solution Helpfull? Yes (2) | No (3)  

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