math question

[shareshab]

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it is known that 20 % o f the population of smallville ha blue eyes . if four people are chosen at random from his populatopn what is the probability that at least one of the four hs blur eyes?

2 . if p<q and r<0 which of the following must be true ?

A. (p+q).r<0
B.(p-q).r<0
C.(q_p).r<0
D.(p-q).r>0
E. R-p-q<0 I think A ,C ,D are coorect but math destroyer says right answer are C and D ????!!
THANKS

 

[UCB05]

it is known that 20 % o f the population of smallville ha blue eyes . if four people are chosen at random from his populatopn what is the probability that at least one of the four hs blur eyes?

2 . if p<q and r<0 which of the following must be true ?

A. (p+q).r<0
B.(p-q).r<0
C.(q_p).r<0
D.(p-q).r>0
E. R-p-q<0 I think A ,C ,D are coorect but math destroyer says right answer are C and D ????!!
THANKS

1) http://forums.studentdoctor.net/showthread.php?t=723650

2)
A. if p ang q are both less than 0, (p+q)<0 and (p+q).r>0. False.
B. for any number, p-q<0. (p-q).r>0. False
C. for any values, q-p>0. (q-p).r<0. True
D. for any values, p-q<0. (p-q).r>0 True
E. r-p-q may be > or < 0 depending on the values of p, q, and r

 

[RCT PC CRN]

This might help.

p<q so (p-q)<0 (small number - big number) always negative. And (q-p)>0 (big number - small number) always positive.

Now combine above with r<0 (negative)

C. (q-p)r<0 (positive)(negative) always <0
D. (p-q)r>0 (negative)(negative) always >0

I didn't spend time analyzing other choices but I think one could follow the trend.

Why are there 2 correct choices?

 

[shareshab]

This might help.

p<q so (p-q)<0 (small number - big number) always negative. And (q-p)>0 (big number - small number) always positive.

Now combine above with r<0 (negative)

C. (q-p)r<0 (positive)(negative) always <0
D. (p-q)r>0 (negative)(negative) always >0

I didn't spend time analyzing other choices but I think one could follow the trend.

Why are there 2 correct choices?

If this is true then choice A should be right as well ??????????😕

 

[Streetwolf]

If this is true then choice A should be right as well ??????????😕

So I guess you didn't read UCB05's post?

Let p = -100, q = -50, and r = -1.

Tell me if A is true.

 

[RCT PC CRN]

You want to look for condition that always true. As UCB05 mentioned the example where A could be false, So A is not your answer. A might be true for certain number but not always. C and D are true for all numbers as long as numbers meet initial condition p<q and r<0. Hope this help.

 

[dentalWorks]

2 . if p<q and r<0 which of the following must be true ?

A. (p+q).r<0
B.(p-q).r<0
C.(q_p).r<0
D.(p-q).r>0
E. R-p-q<0 I think A ,C ,D are coorect but math destroyer says right answer are C and D ????!!
THANKS

What happens when you take a (+) and multiply it by (-)? ALWAYS get negative.

What happens when you take (-) and multiply it by (-)? ALWAYS get positive.

We know that r is (-), we also know that Q is bigger than P (but we don't know their signs).

The only 2 answers that will satisfy ANY sign configuration for P and Q is answer choices C and D.

For answer C
R is (-) and Q-P is (+), multiply them and you will ALWAYS get negative

For answer D
R is (-) and P-Q is (-), multiply them and you will ALWAYS get positive