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Data Sufficiency

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Data Sufficiency

by Tagne » Fri Mar 18, 2011 1:39 pm
1. The sum of positive integers x and y is 77. What is the value of xy?
a. X = y+1
b. X and y have the same tens digit

2. In the xy-plane what is the y intercept of line l?
a. The slope of line L is 3 times the y intercept
b. The x intercept of line L is -1/3

3. If zt < -3, is Z<4?
a. Z<9
b. T<-4
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by Night reader » Fri Mar 18, 2011 2:07 pm
x,y (integers) >0, x+y=77, find xy-?
st(1) x=y+1; (y+1)+y=77, y=38, x=39 Sufficient;
st(2) x and y have the same tens digit. Since x,y >0 the only way for x and y have the same ten digit and their sum being equal to 77 is when x,y have tens digit 3. Now 3A+3B=77 where 3A=x and 3B=y --> 30 +A+30+B=77 OR A+B=17. As A and B are one-digit integers, we can solve for (A+B) only ONE way: A=9, B=8 -hence Sufficient.

IOM D
Tagne wrote:1. The sum of positive integers x and y is 77. What is the value of xy?
a. X = y+1
b. X and y have the same tens digit
Last edited by Night reader on Fri Mar 18, 2011 5:00 pm, edited 1 time in total.
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by Night reader » Fri Mar 18, 2011 2:24 pm
l has line equation y=ax+b, where a is slope, b is y-intercept, Find b-?
st(1) a=3b. For the y-intercept condition we take x=0 and y=0+b. Since x=0 we cannot use slope information --> y=b Not Sufficient;

st(2) x-intercept =-1/3 means y=ax+b, where y=0 and x=-1/3. We need to find b --> 0=(-1/3)*a+b, b=a/3 Not Sufficient, as there is not information about slope.

Combined st(1&2): y=b and b=a/3 --> y=ax+b can be rewritten as b=3bx+b; 3bx=0, we are not given condition for the y-intercept when x=0 hence Either x=0 OR b=0 we don't know, Not Sufficient.

IOM E
Tagne wrote: 2. In the xy-plane what is the y intercept of line l?
a. The slope of line L is 3 times the y intercept
b. The x intercept of line L is -1/3
My knowledge frontiers came to evolve the GMATPill's methods - the credited study means to boost the Verbal competence. I really like their videos, especially for RC, CR and SC. You do check their study methods at https://www.gmatpill.com
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by Night reader » Fri Mar 18, 2011 2:31 pm
zt< -3 means Either z<0, t>0 Or z>0, t<0. Find if z<4?

st(1) z<9, z can be -ve or +ve; Not Sufficient;
st(2) t<-4, t is always -ve Hence z>0. Now z multiplied by t should give <-3 OR (t<-4)*z <-3. If t=-90, z=1/30. If t=<-4 (assumption), z=<3/4. Z cannot be greater than 4, Sufficient.

IOM B
Tagne wrote: 3. If zt < -3, is Z<4?
a. Z<9
b. T<-4
My knowledge frontiers came to evolve the GMATPill's methods - the credited study means to boost the Verbal competence. I really like their videos, especially for RC, CR and SC. You do check their study methods at https://www.gmatpill.com
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by Tagne » Fri Mar 18, 2011 4:34 pm
The answer to question 2 is "D" not "A". Each statement is sufficient. Can any please explain how this is possible?
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by Night reader » Fri Mar 18, 2011 5:01 pm
you mean question No 1, and it was solved for D please check.
thanks
Tagne wrote:The answer to question 2 is "D" not "A". Each statement is sufficient. Can any please explain how this is possible?
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by Tagne » Fri Mar 18, 2011 5:04 pm
Sorry about th error..I meant QUESTION 1 answer is "D"
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by Night reader » Fri Mar 18, 2011 5:11 pm
that's fine, any doubts?
Tagne wrote:Sorry about th error..I meant QUESTION 1 answer is "D"
My knowledge frontiers came to evolve the GMATPill's methods - the credited study means to boost the Verbal competence. I really like their videos, especially for RC, CR and SC. You do check their study methods at https://www.gmatpill.com
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