Latest Infosys Aptitude Question SOLUTION: There are 6561 balls out of them 1 is heavy.Find the min. no. of times the balls have to be weighed for finding out the haevy ball.

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(#M40001126) INFOSYS Logical Reasoning question Keep an EYE

There are 6561 balls out of them 1 is heavy.Find the min. no. of times the balls have to be
weighed for finding out the haevy ball.

Asked In Infosys Naveen (13 years ago)

Solved bvs sharma Read Solution (9)

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bvs sharma  (10 years ago) Best Solution

1)6561/3=2187->2187,2187,2187
2)2187/3=729->729,729,729
3)729/3=243->243,243,243
4)243/3=81->81,81,81
5)81/3=27->27,27,27
6)27/3=9->9,9,9
7)9/3=3->3,3,3
8)3/3=1->1,1,1
8 times required

Is this solution Helpfull? Yes (47) | No (4)  

Vibhu Upadhyaya  (13 years ago)

3^n = N
3^8 = 6561
so ans = 8

Is this solution Helpfull? Yes (28) | No (17)  

Mounika Kosaraju  (10 years ago)

consider 3 balls, u can find the heavier by just weighing 2 balls,now minimum will be 1.Next consider 9 balls, divide them into 3 equal groups, now u can weigh 2 groups to find the group in which the heavier ball lies, and u ll be left with 3 and u know how to find out of 3. so its 3 pow 2 = 9, then 3 pow 3 = 27...... 3 pow 8 = 6561. So the ans is 8.

Is this solution Helpfull? Yes (25) | No (1)  

sandeep  (11 years ago)

Weigh 1/3 of the number of balls against another 1/3.
If they are equal, the heavy ball is in the 1/3 that you didn't weigh.

Each weighing eliminates 2/3 of the number of balls.
6561 = 3*8 so you need 8 weighings.

Is this solution Helpfull? Yes (12) | No (6)  

apoorv tiwari  (9 years ago)

guys why we r dividing it from 3 , can we devide it 9.

Is this solution Helpfull? Yes (11) | No (6)  

Nisheeth Wadhwa  (9 years ago)

why u are taking 3 for power or dividing ?

Is this solution Helpfull? Yes (7) | No (2)  

shivendra pratap singh  (9 years ago)

6561/81=81 times

81/9=9 times

9/9=1 times

so minimum no of times is 3..

Is this solution Helpfull? Yes (7) | No (8)  

sai kamal  (7 years ago)

why three (3) means
let consider the balls divided into a,b,c groups , we know that only one ball is heavier i.e,.. that may be present in a or b or c.
suppose if we measure(compare) a and b groups
if a>b then we know that definately heavy ball is in "a "group
if a

Is this solution Helpfull? Yes (2) | No   

Lokesh Kumar Saini  (8 years ago)

do{ Keep on dividing all balls in 3 groups
Now weigh any two groups
if they are equal
the third group contains the heavy ball
else
the heavier one contains the heavy ball
end
}whlie(we get the only heavy ball)


So number of times we weigh will be log3(6561)=8

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