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kanha81: Master | Next Rank: 500 Posts; Posts: 431; Joined: Sat Jan 10, 2009 9:32 am; Thanked: 16 times; Followed by:1 members

people on board

by kanha81 » Sun Jun 07, 2009 1:16 pm

Half the people on a bus get off at each stop after the first, and no one gets on after the first stop. If only one person gets off at stop number 7, how many people got on at the first stop?

A. 128
B. 64
C. 32
D. 16
E. 8

Want to Beat GMAT.
Always do what you're afraid to do. Whoooop GMAT

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Source: Beat The GMAT — Problem Solving | Sun Jun 07, 2009 1:16 pm

ssmiles08: Master | Next Rank: 500 Posts; Posts: 472; Joined: Sun Mar 29, 2009 6:54 pm; Thanked: 56 times

by ssmiles08 » Sun Jun 07, 2009 1:31 pm

I got (B) as my answer.

If x people got on the bus at 1st stop,

x/2 get off the 2nd stop
x/4 get off the 3rd stop
x/8 - 4th stop
x/16 - 5th stop
x/32 - 6th stop
x/64 - 7th stop

x/64 = 1

x = 64

64 people get on @ the first stop.

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PAB2706: Master | Next Rank: 500 Posts; Posts: 260; Joined: Sun Oct 12, 2008 8:10 pm; Thanked: 4 times

by PAB2706 » Mon Jun 08, 2009 6:22 am

i got 16 as my answer...

wht is the OA?

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kanha81: Master | Next Rank: 500 Posts; Posts: 431; Joined: Sat Jan 10, 2009 9:32 am; Thanked: 16 times; Followed by:1 members

by kanha81 » Mon Jun 08, 2009 6:46 am

PAB2706 wrote:i got 16 as my answer...

wht is the OA?

OA is 64

Want to Beat GMAT.
Always do what you're afraid to do. Whoooop GMAT

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ghacker: Master | Next Rank: 500 Posts; Posts: 148; Joined: Wed Jun 03, 2009 8:04 pm; Thanked: 18 times; Followed by:1 members

by ghacker » Mon Jun 08, 2009 11:36 am

The question is about binary numbers

Lets name the Halts A,B,C,D,E,F and G , G is the final halt , and in other nobody got in but half got out
so if we look at it like this

A B C D E F G
2^6 = 64 .............. 2^0 =1

Ans =2^6 = 64