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Director
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a*b*c*d = 770 a,b,c,d are positive integers a<b<c<d [#permalink]
 20 Jun 2007, 20:24
a*b*c*d = 770
a,b,c,d are positive integers
a<b<c<d
What is c-b if a=1
a) 3
b) 4
c) 5
d) 7
e) 10
I think more than 1 choice works for the above .. wat do u guys say ?
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Senior Manager
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Re: Challenge#23 q25 [#permalink]
20 Jun 2007, 22:12
grad_mba wrote: a*b*c*d = 770
a,b,c,d are positive integers
a<b<c<d
What is c-b if a=1
a) 3
b) 4
c) 5
d) 7
e) 10
I think more than 1 choice works for the above .. wat do u guys say ?
I am getting both 3 and 5 !!
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Director
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bcd = 770 , given that a<b<c<d> c-b = 3
if d is 77, then c = 5, and b = 2 --> c-b = 3
if d is 22, then c= 7, and b = 5 --> c-b = 2
if d is 14, then c= 11, and b = 5 --> c-b = 6
I see the only choice is A. How did you get c-b = 5 ?
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Manager
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me too, I got only 3, hence A.
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Senior Manager
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Mishari wrote: bcd = 770 , given that a<b<c<d> c-b = 3
if d is 77, then c = 5, and b = 2 --> c-b = 3
if d is 22, then c= 7, and b = 5 --> c-b = 2
if d is 14, then c= 11, and b = 5 --> c-b = 6
I see the only choice is A. How did you get c-b = 5 ?
If d=55, c=7 and b=2, then c-b= 5.
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Manager
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my strategy: split in factors
770= 1*2*5*7*11
5 factors, but it has to be 4 (a,b,c,d) and a is 1
so we get 1 * 7 * 10 * 11 (multiply the smallest and re-sort the order)
c-b = 10-7 = 3
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Manager
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ronron wrote: my strategy: split in factors
770= 1*2*5*7*11
5 factors, but it has to be 4 (a,b,c,d) and a is 1
so we get 1 * 7 * 10 * 11 (multiply the smallest and re-sort the order)
c-b = 10-7 = 3
There are numerous 3 digit products that = 770.
I also used prime factorization 770 and got 2, 5, 7, 11.
so if:
b = 2 c = 5 d = 77 c - a = 5 - 2 = 3
However,
if we use 7 then:
b = 2 c = 7 d = 55 c - a = 5
I also get A and C.
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Senior Manager
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Re: Challenge#23 q25 [#permalink]
22 Jun 2007, 21:23
grad_mba wrote: a*b*c*d = 770
a,b,c,d are positive integers
a<b<c<d
What is c-b if a=1
a) 3
b) 4
c) 5
d) 7
e) 10
I think more than 1 choice works for the above .. wat do u guys say ?
having worked through a few challenges i am very skeptical of some of the challenge questions; for $80 it is the most expensive lot of practice tests i have paid for and it is obvious they were not written by professional test writers - the explanations to some of the questions are just abysmal. this is a prime example; you can get two answers. i actually went shoonya's route on this one and started plugging in #s from the middle answer choice... and got 5  but i see 3 works too.
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Re: Challenge#23 q25
[#permalink]
22 Jun 2007, 21:23
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