2.
Is a+2b<c+2d?
1) a<c
2) d>b
[spoiler]
Adding statement 1 and 2
a < c
b < d
a+b< c+d
(we can add another b<d.....why?)
a+2b <c+2d[/spoiler]
Combining Inequalities
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- albatross86
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Each statement on it's own is insufficient, as it does not provide sufficient info about all 4 variables.
Both Statements together:
a < c
b < d (You can flip an inequality like this)
When combining 2 inequalities make sure that:
1. You have oriented them such that they have the same symbol ( < , >, etc)
2. You are adding them. DO NOT subtract.
Adding these two inequalities gives us :
a + b < c + d
This is a third inequality. But to get it to answer our prompt, we need to manipulate it a bit more. Technically you can keep adding inequalities to eachother as long as you follow those 2 rules.
Thus we could add our inequality b < d to the above again, to get to our prompt.
a + 2b < c + 2d
For a quick revision of the basic rules of dealing with inequalities, refer to this link:
https://www.platinumgmat.com/gmat_study_ ... equalities
Both Statements together:
a < c
b < d (You can flip an inequality like this)
When combining 2 inequalities make sure that:
1. You have oriented them such that they have the same symbol ( < , >, etc)
2. You are adding them. DO NOT subtract.
Adding these two inequalities gives us :
a + b < c + d
This is a third inequality. But to get it to answer our prompt, we need to manipulate it a bit more. Technically you can keep adding inequalities to eachother as long as you follow those 2 rules.
Thus we could add our inequality b < d to the above again, to get to our prompt.
a + 2b < c + 2d
For a quick revision of the basic rules of dealing with inequalities, refer to this link:
https://www.platinumgmat.com/gmat_study_ ... equalities
~Abhay
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Believe those who are seeking the truth. Doubt those who find it. -- Andre Gide
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is a+2b<c+2d
a-c<2*(d-b)
(1) a<c, a-c<0 it means that left part of the inequality is - ve but no info about (d-b)
so 1 st insufficient
(2) here (d-b)>0 but no about (a-c) insufficient
together
(a-c)<0 and (d-b)>0, -ve number is always less that +ve so the answer must be C (to me)
a-c<2*(d-b)
(1) a<c, a-c<0 it means that left part of the inequality is - ve but no info about (d-b)
so 1 st insufficient
(2) here (d-b)>0 but no about (a-c) insufficient
together
(a-c)<0 and (d-b)>0, -ve number is always less that +ve so the answer must be C (to me)