It takes 30 days to fill a laboratory dish with bacteria. If the size ofthe bactiria doubles each day, how long did it take for the bactiria to fill one half of dish?

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  • Mar 6th, 2006

It'll take 29 days to fill half.

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nithiya devi

  • Mar 21st, 2006

the answer is 29 days

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mohan kumar

  • May 19th, 2006

seven and a half days

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  • Jul 24th, 2006


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Kmalesh malviya

  • Jul 27th, 2006

Obviosly it will take 29 days ,since on the 30th day it will be doubled and get filled...


  • Aug 10th, 2006

In 30th day the bacteria is completely filled in the dish and per day the size is doubled. Hence at 29th day the dish must me half. So the ans is 29 days.Send me some recent wipro placementpapers.

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  • Sep 17th, 2006

yes it is 29 days

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Brijesh Kumar

  • Apr 7th, 2007

see                               firstday -> x
    then second day it becomes ->2x
      then third days                   ->4x
                              ans so on  8x , 16x , 32x then it ll cross 60 , when it has 64 x...
   then   it takes more than 7 days

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  • Apr 27th, 2007

 it takes 7 and a half days to fill the dish

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  • Jul 1st, 2007

Preethi here is the solution

Suppose a 30kg container will be filled in 30 days by putting 1kg bacteria on each day
On first day 1kg is put into the dish in 30 kgs.

Second day it will be doubled 2+second days 1kg

Third day it will be 6kgs+third day 1kg
Fourth day it will be 14kgs+1kg

Fifth day it will be 30kgs

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  • Aug 20th, 2007

29 will be the correct answer. We have to go from the bottom. On the 29th day it will be half of the tank since on the 30th day it is filled.

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  • Oct 9th, 2007

First day: 1
2nd day: 2+1 (it doubles 1 to 2 and +1 for the day)
3rd day: 6+1 (it doubles 3 to 6 and +1 for the day)
So on..

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  • Mar 15th, 2008

1st day 372.529% of bacteria is filled
2nd day 745.05%
by this way on 29th day 50% is filled
and the last day 100% bacteria is filled

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  • May 22nd, 2008

1st day it fills 1/30
2nd day it fils 1/30+2/30
3rd day it fills 1/30+2/30+4/30
4th day it fills 1/30+2/30+4/30+8/30=1/2

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  • Oct 15th, 2011

Let A1 -> increased area
A-> original area

A1=1.69%(since it is increased by 69%)

1.69 S^2=S1^2
S1->increased side
S->original side

therefore taking square root on both sides
1.3 S=S1
therefore s is increased by .3 i.e 30%

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