# N positive integer problem with a + exponent

Printable View

• Mar 24th 2010, 09:01 AM
artabro
N positive integer problem with a + exponent
Here it is a problem that is driving me nuts...
Note: ^ means the exponent, in this case the exponent is "+".
If n is a positive integer, then n^+ denotes a number such that n < n^+ < n+1.

So decide which of the following options is greater (or if both ofthem are equal or if it is impossible to determine it).

Option A: 20^+ / 4^+

Option B: 5^+

What I did: 20^+ / 4^+ SO, (20/4)^+ , SO (5)^+ , so I concluded that both of them are equal, but the correct answer is " It canīt be determined which option is greater". Could anyone explain me why??
• Mar 24th 2010, 10:14 AM
Anonymous1
We have:

$20< 20^+ < 21$

$4< 4^+ < 5$

$5<5^+<6$

Clearly we cannot divide these inequalities.

$\frac{20< 20^+ < 21}{4< 4^+ < 5} = ???????$

But we can determine bounds.

How do we obtain the smallest possible value of $\frac{20^+}{4^+}?$ We minimize the numerator and maximize the denominator. The numerator's smallest value is close to $20,$ and the denominator's largest value is close to $5.$ So, the fractional value is $\frac{20^+}{4^+}> \frac{20}{5}=4$.

Now, How do we obtain the largest possible value of $\frac{20^+}{4^+}?$ We maximize the numerator and minimize the denominator. We would end up with $\frac{20^+}{4^+} < \frac{21}{4} = 5.25.$

So, $4<\frac{20^+}{4^+}<5.25,$ Which could be greater or less than $5 <5^+<6$ depending on which value $5^+$ were to take on.
• Mar 24th 2010, 10:22 AM
Deadstar
Quote:

Originally Posted by artabro
Here it is a problem that is driving me nuts...
Note: ^ means the exponent, in this case the exponent is "+".
If n is a positive integer, then n^+ denotes a number such that n < n^+ < n+1.

So decide which of the following options is greater (or if both of them are equal or if it is impossible to determine it).

Option A: 20^+ / 4^+

Option B: 5^+

What I did: 20^+ / 4^+ SO, (20/4)^+ , SO (5)^+ , so I concluded that both of them are equal, but the correct answer is " It canīt be determined which option is greater". Could anyone explain me why??

Okay, here's how I'm looking at it.
The + sign means you add on some fractional part that is greater than 0 but less than 1 onto n.

The problem I'm seeing with the question is that, if we take two numbers, say 3 and 4,

Does $3^+$ and $4^+$ mean that the SAME fractional part gets added on to both 3 and 4? Or does it mean some random fractional part gets added on?

If its the first option... Than option B is greater since for option A you have...
$\frac{21}{5} < \frac{20^+}{4^+} < \frac{20}{4} = 5$

while for option B you have
$5 < 5^+ < 6$

Clearly option B is larger.

If the + sign means you add on a random fractional part as I think it probably is...

Then you cant conclude that either is bigger.

As an example...
Take $20^+ = 20.99$, $4^+ = 4.01$ and $5^+$ to be 5.01

Than for option A you get
roughly 5.23
and for B you get
5.01
Hence A is bigger

Now take $20^+ = 20.01$, $4^+ = 4.99$ and $5^+$ to be 5.99

Then for option A you get
4.01
and for B you get
5.99
So B is bigger.
• Mar 25th 2010, 02:21 PM
Anonymous1
Actually, this question reminds me of techniques used in elementary $Real$ $Analysis.$