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Re: PS: Greatest Common Factor [#permalink]
15 Mar 2008, 14:44

The answer should be 10. If x/2 and y/2 have the GCF of 5, it means that x/2 and y/2 should both be divisible by 5. This implies that x and y should both be divisible by 10. As an example you can take 10 and 20 or 20 and 30 or 30 and 40 and so on. If you take alternate 10s like 20 and 40, then 10 and 20 do not have the GCF of 5 but have the GCF of 10. That contradicts our first condition. rkassal

Re: PS: Greatest Common Factor [#permalink]
24 May 2011, 04:43

ok so i agree statement 2 is insufficient, however i do have a quick question regarding statement 1, you have said if x/2 and y/2 have a GCF of 5, then the GCF of x and y is 10. However i didnt really apply the straight forward technique so need your help here, please find below my technique

assuming x= 20 y=10

x/2= 10 y/2= 5

10= 2*5 5= 5*1

Hence GCF would be the common numbers with the lowest exponent, i.e. 5^1=5.