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Re: If d > 0 and 0 < 1 - c/d < 1, which of the [#permalink]
01 Apr 2012, 12:09

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mymbadreamz wrote:

I didn't understand this. could someone explain? thanks.

If d >0 and 0 < 1 - \frac{c}{d} < 1, which of the following must be true?

I. c > 0 II. \frac{c}{d} < 1 III. c^2 + d^2 > 1

A. I only B. II only C. I and II only D. II and III only E. I, II, and III[/quote]

0<1-\frac{c}{d}<1 --> add -1 to all three parts of this inequality --> -1<-\frac{c}{d}<0 --> mutliply by -1 and as multiplying by negative flip signs --> 1>\frac{c}{d}>0.

So we have that: 1>\frac{c}{d}>0

I. c>0 --> as \frac{c}{d}>0 and d>0, then c>0. Always true.

II. \frac{c}{d}<1 --> directly given as true.

III. c^2 + d^2 > 1 --> if c=1 and d=2, then YES, but if c=0.1 and d=0.2, then No, hences this one is not always true.

Re: If d > 0 and 0 < 1 - c/d < 1, which of the following must be [#permalink]
02 Apr 2012, 17:18

kashishh wrote:

Inequalities !! is it possible to get some tips and tools to solve these "sign" (< = > ) questions?

i dunno if my method can help you but i solved it in two ways.

0 < 1 - (c/d) < 1

the way i looked at this problem was to first simply the equation by subtracting 1 in the middle to both sides: -1 < -(c/d) < 0

and the given statement is that d is greater than zero, so d must be positive. if we know a variable is positive, you can safely multiply the variable without changing the signs. so i multiplied d to isolate c. -1(d) < -c < 0(d)

so we get -d < -c < 0

and then i divided the negative out and switched the signs. d > c > 0

the above answers statement I. c > 0 is true. for statement II, i manipulated the above equation by dividing d and i get 1 > c/d > 0 this answers statement II. c/d < 1

the last statement i just tested numbers using the d > c > 0 by using whole numbers and decimals.

the second way i solved this was using bunuel's way.