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SETS - DS query

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by MI3 » Mon May 16, 2011 12:02 pm
Q. If none of the students are ambidextrous, what percentage of the 20 students in Mr. Henderson's class are
left-handed?
(1) Of the 12 girls in the class, 25% are left-handed.
(2) 5 of the boys in the class are right-handed.

I chose answer C, am I correct?
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by pankajks2010 » Mon May 16, 2011 6:30 pm
the question itself provides the total number of students. Now, we need to know, how many girls/boys are left-handed.

Statement 1: provides information on girls only, thus, we don't get any hint on the number of boys who are left-handed. Insufficient

Statement 2: As like above, this too is just focussed on boys and no information on girls Insufficient

Combining both: 25% of girls are left handed; ie; 3 girls are left handed. From (2), 5 boys are left-handed. Now, we have the total lefties in the class Sufficient

C
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by jerseyny » Fri May 20, 2011 7:43 pm
Hi pankajks2010, I have a question though.

The 2nd given condition says that 5 boys are right-handed, not left-handed.

I get that there are total 20 students in the class,
Among 12 girls 3 are left-handed, 9 are right-handed
and that 5 boys are right-handed. In this condition, can we assume that the left over 3 people are boys that are left-handed?

These type of questions confuse me. If we can assume that I guess the answer is C but I thought we can't make that assumption so I thought it was E.
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by uslalas22 » Fri May 20, 2011 8:15 pm
Jerseyny,

Since statement 1) states "of the 12 girls" it tells us there are 12 girls in the class. If it just said "12 of the girls" (yes a simple switch of words coincidentally) then we wouldn't know the full number of girls and therefore the full number of boys.

Also since it notes that no on is "ambidextrous" it means that none of the students could possibly right with both. So they are either boy or girl, and either right or left handed.

So putting both together we have as you noted 3 left handed girls, 9 right handed girls, 5 right handed boys, 3 left handed boys.
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by pankajks2010 » Sat May 21, 2011 1:06 am
jerseyny wrote:Hi pankajks2010, I have a question though.

The 2nd given condition says that 5 boys are right-handed, not left-handed.

I get that there are total 20 students in the class,
Among 12 girls 3 are left-handed, 9 are right-handed
and that 5 boys are right-handed. In this condition, can we assume that the left over 3 people are boys that are left-handed?
Here the question clearly states that no one in the class is ambidextrous. Thus, we are not making any assumptions here...

I can understand your situation, even, I have got many questions wrong while being over-cautious.

Hope this helps!!
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