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20 Mar 2012, 09:07
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E
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78% (00:52) correct
22%
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Is x less than 20?
(1) The sum of x and y is less than 20.
(2) y is less than 20.
(1) The sum of x and y is less than 20.
(2) y is less than 20.
20 Mar 2012, 09:17
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enigma123
Is x < 20?
1. Sum of x and y is less than 20
2. y is less than 20
How come the answer is E and not A?
1. Sum of x and y is less than 20
2. y is less than 20
How come the answer is E and not A?
Consider two cases:
x=30 and y=-15;
x=15 and y=-15;
Both examples satisfy the statements and give different answers to the question whether x<20. Not sufficient.
Answer: E.
02 Mar 2014, 04:20
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mariofelix
but if we solve it like this:
subtract
x+y < 20
y < 20
x+y-y<0
x<0
then x will be certainly less than 20...
Why is this approach flawed ?
Consider two cases:
x=30 and y=-15;
x=15 and y=-15;
Both examples satisfy the statements and give different answers to the question whether x<20. Not sufficient.
Answer: E.
subtract
x+y < 20
y < 20
x+y-y<0
x<0
then x will be certainly less than 20...
Why is this approach flawed ?
Bunuel
enigma123
Is x < 20?
1. Sum of x and y is less than 20
2. y is less than 20
How come the answer is E and not A?
1. Sum of x and y is less than 20
2. y is less than 20
How come the answer is E and not A?
Consider two cases:
x=30 and y=-15;
x=15 and y=-15;
Both examples satisfy the statements and give different answers to the question whether x<20. Not sufficient.
Answer: E.
That's wrong because you cannot subtract inequalities with signs in the same direction.
ADDING/SUBTRACTING INEQUALITIES:
You can only add inequalities when their signs are in the same direction:
If \(a>b\) and \(c>d\) (signs in same direction: \(>\) and \(>\)) --> \(a+c>b+d\).
Example: \(3<4\) and \(2<5\) --> \(3+2<4+5\).
You can only apply subtraction when their signs are in the opposite directions:
If \(a>b\) and \(c<d\) (signs in opposite direction: \(>\) and \(<\)) --> \(a-c>b-d\) (take the sign of the inequality you subtract from).
Example: \(3<4\) and \(5>1\) --> \(3-5<4-1\).
Adding/subtracting/multiplying/dividing inequalities: help-with-add-subtract-mult-divid-multiple-inequalities-155290.html
Hope it helps.
