inequality

[tanviet]

this is a official question from retired test and should be studied

if x and y are positive, is 3x>7y?

a, x>y+4

b, -5x<-14y

[aj5105]

I got (E)

Take values, (x = 6 y = 1) for yes & (x = 15 y = 10) for no

[shilpi84]

this is a official question from retired test and should be studied

if x and y are positive, is 3x>7y?

a, x>y+4

b, -5x<-14y

IMO B

Taking the first statement:
given:x>y+4 plug in values x = 10 y = 1 then 3x>7y
x = 10 y = 2 then 3x>7y
x = 10 y = 3 then 3x>7y
x = 10 y = 4 then 3x>7y
x = 10 y = 5 then 3x<7y
So, stmt 1 is not sufficient.

Taking the second statement:
given: -5x<-14y
x/y>14/5
x/y > 2.8
if it is greater than 2.8 it has to be greater than 2.3
hence statement 2 is sufficient.

Some1 got a faster method?

[aj5105]

Solution from maihuna

If x and y are positive, is 3x > 7y?
(1) x > y + 4
(2) -5x < -14y

One is saying x-y >4 so nothing can really be concluded. See below:

x = 6 , y = 1 x-y = 5 3x = 18, 7y = 7 so 3x>7y
x = 20, y = 15, x-y = 5>4, 3x = 60, 7y = 105 so 3x<7y

2. 5x>14y
if 3x>7y => 6x>14y since we know 5x>14y we can say 6x>14y so 2 solve it

Ans: B

[cramya]

is 3x>7y

is x>2.3333...y

Stmt I

x>y+4

The question is Is 4>1.333333y

We can have y values satisfying this and not

INSUFF

Stmt II

-5x<-14y

Divide by -5 on both sides the inequality reverses

x>14/5y
x>2.8y

Definitely x>2.33333...y

B

[tanviet]

can we sumarize this kind as following

question x>F1(y)?

given x> F2(y)

we have to find weather "F2 > F1. if F2>F1, we have yes, oppsite we have no answer.

is that right?