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Can we solve logically without using GP formula?

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Can we solve logically without using GP formula?

by [email protected] » Tue Oct 29, 2013 3:14 am
The population of locusts in a certain swarm doubles every two hours. If 4 hours ago there were 1,000 locusts in the swarm, in approximately how many hours will the swarm population exceed 250,000 locusts?
A) 6
B) 8
C) 10
D) 12
E) 14

Ans 12
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by Uva@90 » Tue Oct 29, 2013 4:11 am
[email protected] wrote:The population of locusts in a certain swarm doubles every two hours. If 4 hours ago there were 1,000 locusts in the swarm, in approximately how many hours will the swarm population exceed 250,000 locusts?
A) 6
B) 8
C) 10
D) 12
E) 14

Ans 12
Shibriz
4 Hours back Population is 1000
It will get Doubles every two hours
So, 2 hours back Population would have been 2000
and now it is 4000

So 4000*(2^x) > 250,000(In question it is asked when it will exceed that why > symbol)
2^x > 62.5
Note: X should be an integer

X takes 6(2^6 =64)

So it is multiplied 6 times hence 6*2 = 12 Hours.

Hope it helps you.

Regards,
Uva
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by GMATGuruNY » Tue Oct 29, 2013 4:41 am
[email protected] wrote:The population of locusts in a certain swarm doubles every two hours. If 4 hours ago there were 1,000 locusts in the swarm, in approximately how many hours will the swarm population exceed 250,000 locusts?
A) 6
B) 8
C) 10
D) 12
E) 14

Ans 12
WRITE IT OUT.
4 hours ago, the population = 1000.
Every 2 hours, the population doubles.

4 hours ago --> 1000
2 hours ago --> 2000
Now --> 4000
2 hours from now --> 8000
4 hours from now --> 16000
6 hours from now --> 32000
8 hours from now --> 64000
10 hours from now --> 128000
12 hours from now --> 256000

The correct answer is D.
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