Problem Solving Question

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Problem Solving Question

by Saup » Sun Jan 19, 2020 10:38 am
If 0<r<1<s<2, which of the following must be less than 1?

I. \frac{r}{s}
II. rs
III. s-r

A. I only
B. II only
C. III only
D. I and II
E. I and III

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Re: Problem Solving Question

by Saupayan » Sun Jan 19, 2020 11:04 am
Answer : A
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Re: Problem Solving Question

by [email protected] » Sun Feb 23, 2020 9:47 am
Saup wrote:
Sun Jan 19, 2020 10:38 am
If 0<r<1<s<2, which of the following must be less than 1?

I. r/s
II. rs
III. s-r

A. I only
B. II only
C. III only
D. I and II
E. I and III
I) r/s
r and s are both POSITIVE, and r is less than s.
So, it MUST be the case that r/s < 1


II) rs
It could be the case that r = 0.9 and s = 1.8, in which case rs = 1.62
So, it NEED NOT be the case that rs < 1

III) s - r
It could be the case that r = 0.1 and s = 1.8, in which case s - r = 1.7
So, it NEED NOT be the case that s - r < 1

Answer: A

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Brent
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Re: Problem Solving Question

by gmatknight » Wed Feb 26, 2020 12:59 am
The best way to solve this problem is to pick a set of variables that meet the conditions of R and S and play around with them. The question asks what MUST be less than 1. Use that statement as your anchor. Ask yourself if, with the variables you have chosen, if it is even possible to make an answer greater than 1.

I'd also recommend you use the answer choices to shorten your time, but it would probably be best to understand the concept at play here first for those unfamiliar with this type of question. (For example, if you know for certain that statement (1) and (3) must be less than 1, you don't need to worry about figuring out (2): the answer choices don't have all three choices as an option!)
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Re: Problem Solving Question

by PhillipZhang87 » Fri Sep 18, 2020 5:28 am
The best approach for a lot of algebra questions like these is to definitely to pick numbers and think logically.
I r/s we know 0< numerator < 1 as well as, 1 < denominator < 2 so the answer definitely be less than 1.
II rs choose r = 0.2 s = 1.1 rs = 0.22 < 1 so not the case
III s - r choose r = 0.9 s = 1.1 1.1 - 0.9 = 0.2 so < 1
Therefore, A is correct answer.