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set of numbers

by rahul.s » Sun Jan 31, 2010 6:25 am
R is a set of numbers such that

if m is in R, then -2m is in R, and
if each of m and n is in R, then mn is in R.
Is 60 in R?

1) 3 is in R.
2) 5 is in R.

OA: C
Last edited by rahul.s on Sun Jan 31, 2010 7:44 am, edited 1 time in total.
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Source: — Data Sufficiency |
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by ajith » Sun Jan 31, 2010 6:37 am
rahul.s wrote:R is a set of numbers such that

if m is in R, then -2m is in R, and
if each of m and n is in R, then mn is in R.
Is 60 in R?

1) 3 is in R.
2) 5 is in R.

OA: C

1) 3 is in R

Is not sufficient since it is helpful in proving, 3, -6, -18, 12...etc (none of these factors have prime factors other than 2&3)

So 60 is not an option since 60 has prime factors 2,3 and 5

2)Is not sufficient since it is helpful in proving, 5, -10, -50, 20 ...etc (none of these factors have prime factors other than 2&3)

So 60 is not an option since 60 has prime factors 2,3 and 5

combining 1&2

3 and 5 are in R -- 15 is in R ; -30 is in R ; 60 is in R
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by thephoenix » Sun Jan 31, 2010 7:30 am
ajith wrote:
rahul.s wrote:R is a set of numbers such that

if m is in R, then -2m is in R, and
if each of m and n is in R, then mn is in R.
Is 60 in R?

1) 3 is in R.
2) 5 is in R.

OA: C

1) 3 is in R

Is not sufficient since it is helpful in proving, 3, -6, -18, 12...etc (none of these factors have prime factors other than 2&3)

So 60 is not an option since 60 has prime factors 2,3 and 5

hi ajit y at this point we can not say that no 60 is not in R and therefore this statement is suff.????



2)Is not sufficient since it is helpful in proving, 5, -10, -50, 20 ...etc (none of these factors have prime factors other than 2&3)

So 60 is not an option since 60 has prime factors 2,3 and 5

combining 1&2

3 and 5 are in R -- 15 is in R ; -30 is in R ; 60 is in R
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by ajith » Sun Jan 31, 2010 10:10 am
thephoenix wrote:
So 60 is not an option since 60 has prime factors 2,3 and 5

hi ajit y at this point we can not say that no 60 is not in R and therefore this statement is suff.????
Nope, You don't know whether 5 is in R or not

All you know is 3 is in R, 5 may or may not be in R and thus we cannot say No to the question
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by rahul.s » Sun Jan 31, 2010 9:44 pm
if m is in R, then -2m is in R.
and if m and n are in R, then mn are in R

statement 1

hence, 3, -6, 12, -24, 48, -96, so on and so forth. insufficient.

statement 2

5, -10, 20, -40, 80, -160 et cetera. insufficient

combining

3 and 5 are in R.

mn are in R

hence, 15, -30, 60.
sufficient.
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