Integers

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moneyman: Master | Next Rank: 500 Posts; Posts: 468; Joined: Sat Mar 03, 2007 10:17 pm; Thanked: 5 times

by moneyman » Sun Oct 21, 2007 2:41 am

If x and y are positive integers , what is the value of xy??

(1)The greatest common factor of x and y is 10
(2)The least common multiple of x and y is 180

Maxx

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Source: Beat The GMAT — Problem Solving | Sun Oct 21, 2007 2:41 am

samirpandeyit62: Master | Next Rank: 500 Posts; Posts: 460; Joined: Sun Mar 25, 2007 7:42 am; Thanked: 27 times

by samirpandeyit62 » Sun Oct 21, 2007 4:16 am

If x and y are positive integers , what is the value of xy??

(1)The greatest common factor of x and y is 10

can be 20,30 30,50 etc INSUFF

(2)The least common multiple of x and y is 180

180 = 9 * 2 * 5 * 2

it can be 90,20 180,10 etc insuff

combine: here also we cannot say coz both these pairs have 10 as GCD

E

Regards
Samir

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agni_mba: Junior | Next Rank: 30 Posts; Posts: 18; Joined: Mon Aug 13, 2007 3:04 am; Location: india

by agni_mba » Sun Oct 21, 2007 2:06 pm

I think the answer should be C.

10 GCD => X/10, Y/10 will be that part of X, Y which are uncommon between the two. This means if we multiply these two with 10, that would give me LCM.

i.e. X*Y/10 = 180 or X.Y=1800.

cheers

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gmatguy16: Master | Next Rank: 500 Posts; Posts: 124; Joined: Thu Aug 23, 2007 5:11 am; Thanked: 2 times

by gmatguy16 » Sun Oct 21, 2007 3:40 pm

samir why do you think this rule does not apply here ,
gcd*lcm of two integers = product of two integers

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ri2007: Master | Next Rank: 500 Posts; Posts: 258; Joined: Mon Aug 27, 2007 12:43 pm; Thanked: 15 times

by ri2007 » Sun Oct 21, 2007 7:16 pm

samirpandeyit62 wrote:If x and y are positive integers , what is the value of xy??

(1)The greatest common factor of x and y is 10

can be 20,30 30,50 etc INSUFF

(2)The least common multiple of x and y is 180

180 = 9 * 2 * 5 * 2

it can be 90,20 180,10 etc insuff

combine: here also we cannot say coz both these pairs have 10 as GCD

E

Samir

Should the ans not be C?
Since we know GCF is 10 and LCM is 180 the only numbers possible are 10*2 and 10*9 or 10*18 and 10*1

product of both these pairs is the same 1800

To be honest once u write an ans i have developed a tendency not to question it...since its usually right:)) but would appreciate if u could take a look at it again

thanks

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samirpandeyit62: Master | Next Rank: 500 Posts; Posts: 460; Joined: Sun Mar 25, 2007 7:42 am; Thanked: 27 times

by samirpandeyit62 » Sun Oct 21, 2007 8:56 pm

My bad, I somehow thought that we need values of x & y (did not have good concentration) but we require xy here so 90,20 & 180,10 will give the same results, so C should be the ans, Thanks agni_mba, gmatguy16 & RI for pointing out.

RI : As human beings no body is infallible & so am I, so please go ahead & correct me if I'm wrong, I would really appreciate that, thanks.

Regards
Samir

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