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Re: What is the value of 0.1 + 0.1^(1/m) + 0.1^(1/n) ? [#permalink]
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KSBGC wrote:
What is the value of \(0.1 + 0.1^{\frac{1}{m}} + 0.1^{\frac{1}{n}}\)?


(1) \(\frac{1}{m}+ \frac{1}{n} = \frac{4}{3}\)

(2) mn = 3.

Solution:
Pre Analysis:
  • We are asked the value of \(0.1 + 0.1^{\frac{1}{m}} + 0.1^{\frac{1}{n}}\)
  • This cannot be simplified in any way where any one statement will be sufficient
  • We need the value of both m and n to get the answer

Statement 1: \(\frac{1}{m}+ \frac{1}{n} = \frac{4}{3}\)
\(⇒\frac{n+m}{mn}=\frac{4}{3}\)
  • We cannot get the value of m and n from this
  • Thus, statement 1 alone is not sufficient and we can eliminate options A and D

Statement 2: mn = 3
  • We cannot get the value of m and n from this
  • Thus, statement 2 alone is also not sufficient and we can eliminate option B

Combining:
  • From statement 1, we have \(\frac{n+m}{mn}=\frac{4}{3}\)
    \(⇒\frac{n+m}{3}=\frac{4}{3}\) (from statement 2)
    \(⇒n+m=4\)
    \(⇒\frac{3}{m}+m=4\)
    \(⇒\frac{3+m^2}{m}=4\)
    \(⇒m^2-4m+3=0\)
  • The values of m are 3 and 1
  • When m = 3, \(n=\frac{3}{m}=\frac{3}{3}=1\)
  • When m = 1, \(n=\frac{3}{m}=\frac{3}{1}=3\)

  • When (m, n) = (3, 1), the value of \(0.1 + 0.1^{\frac{1}{3}} + 0.1^{\frac{1}{1}}=0.2+0.1^{\frac{1}{3}}\)
  • When (m, n) = (1, 3), the value of \(0.1 + 0.1^{\frac{1}{1}} + 0.1^{\frac{1}{3}}=0.2+0.1^{\frac{1}{3}}\)

Hence the right answer is Option C
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Re: What is the value of 0.1 + 0.1^(1/m) + 0.1^(1/n) ? [#permalink]
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selim wrote:
What is the value of \(0.1 + 0.1^{1/m} + 0.1^{1/n}\)?

1) \(1/m + 1/n = 4/3\)

2) mn = 3.



\(0.1 + 0.1^{\frac{1}{m}} + 0.1^{\frac{1}{n}}=\frac{1}{10} + \frac{1}{10}^{\frac{1}{m}} + \frac{1}{10}^{\frac{1}{n}}=\frac{10^{m+n}+10^{m+1}+10^{n+1}}{10^{m+n+1}}\)
So, we require values of m and n..

When we combine statement 1 and statement 2, we get m and n as 1 and 3 in any order. When we substitute (m =3 and n=1) or (m=1 and n=3), we will get the same answer.
\(\frac{10^{m+n}+10^{m+1}+10^{n+1}}{10^{m+n+1}}=\frac{10^{1+3}+10^{1+1}+10^{3+1}}{10^{1+3+1}}=\frac{10^4+10^2+10^4}{10^5}=\frac{20100}{100000}=\frac{201}{1000}\)=0.201

C
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Re: What is the value of 0.1 + 0.1^(1/m) + 0.1^(1/n) ? [#permalink]
Can someone please explain this in detail!?

Posted from my mobile device
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Re: What is the value of 0.1 + 0.1^(1/m) + 0.1^(1/n) ? [#permalink]
KSBGC wrote:
What is the value of \(0.1 + 0.1^{\frac{1}{m}} + 0.1^{\frac{1}{n}}\)?


(1) \(\frac{1}{m}+ \frac{1}{n} = \frac{4}{3}\)

(2) mn = 3.



Since we have m and n as exponents in two separated terms from the equation, and those terms are being added together (so we cannot "merge" them like if they were being multiplied), we will need to figure out a way to find both \(m\) as well as \(n\).

(1) gives us one equation with 2 variables. This is not enough to solve for both of them, and thus is insufficient.

(2) gives us, again, one equation with 2 variables. Insufficient.

(1) + (2) gives us two equations for two variables, which can be solved. \(\frac{1}{m}+ \frac{1}{n} = \frac{m + n}{mn} = \frac{4}{3}\).
From this, \(m+n = 4\), and \(m = (4 - n)\).

\(m * n = 3\)

\((4 - n) * n = 3\)

\(n^2 - 4n + 3 = 0\)

\(n = 3\) or \(n = 1\).


If n = 3, m = 1. On the other hand, if n = 1, m = 3.

Now, since the terms to the power of \(\frac{1}{m}\) and \(\frac{1}{n}\) are both at the same base (\(0.1\)), it doesn't matter whether \((m,n) = (1,3)\) or \((m,n) = (3,1)\). Both will give the same final result, and this means that (1) and (2) together are sufficient.

Answer is C.
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