Mathematics · Quantitative Aptitude

Logarithms

231 Questions

Logarithms are mathematical operations that determine the exponent required for a base to reach a specific number. This topic tests the application of logarithmic properties, changing bases, and solving complex equations. It is a high-yield topic for quantitative aptitude in competitive exams.

Logarithmic expressionsBase change propertiesSolving log equationsInfinite series logsCharacteristic values

Logarithms Questions

Multiple choice logarithm and its uses basic mathematical concepts physics

Let $A=\dfrac{1}{6}((\log _{2}{3}))^{3}-(\log _{2}{6}))^{3}-(\log _{2}{12}))^{3}+(\log _{2}{24}))^{3})$. Then the value of $2^{A}$ is :

  1. $72$
  2. $70$
  3. $68$
  4. $None\ of \ these$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Using log properties and the identity (x-y)^3 = x^3 - 3x^2y + 3xy^2 - y^3, the expression simplifies to a value that results in 2^A = 72.

Multiple choice logarithm and its uses basic mathematical concepts physics

Find the mantissa of the logarithm of the number $0.002359$.

  1. $3710$
  2. $3718$
  3. $3728$
  4. $3742$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

We have to find $\log (0.002359)$

Firstly, we will write $0.002359$ in standard form.
So, $0.002359 = 2.359 \times 10^{-3}$
Here, characteristic is -3.

To find the mantissa of $\log (0.002359)$, we first look in the row starting with 23. In this row, look at the number in the column headed by 5. The number is 3711.

Now, move to the column of mean differences and look under the column headed by 9 in the row corresponding to 23. We see the number 17 here.

Add this number to 3711. We get the number 3728. This is the required mantissa of $\log (0.002359)$.

Mantissa of $\log 23.598$, $\log 2.3598$ and 0.023598 is the same (only characteristics are different).

Multiple choice logarithm and its uses basic mathematical concepts physics

The value of $\displaystyle \log _{\frac{1}{20}}40$ is

  1. greater than zero.

  2. smaller than zero.

  3. greater than zero and smaller than one.

  4. none of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let,  $y=\displaystyle \log _{\frac{1}{20}}40$
$\Rightarrow y=-\displaystyle \log _{20}40 \quad [\because \log _{1/a}b=-\log _ab]$
Now $20 < 40<20^2\Rightarrow \log _{20}20<\log _{20}40<\log _{20}20^2$
$\Rightarrow 1< \log _{20}40<2 \quad [\because \log a^m=m\log a, \log _aa=1]$
$\Rightarrow 1<-y<2\Rightarrow -2<y<-1$

Multiple choice logarithm and its uses basic mathematical concepts physics

The value of $\displaystyle \log _{\frac{2}{3}}\frac{5}{6}$ is

  1. less than zero.

  2. greater than zero and less than one.

  3. greater than one.

  4. none of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$\displaystyle \frac { 2 }{ 3 } <\frac { 5 }{ 6 } <1$
Taking log with base $\displaystyle \frac { 2 }{ 3 } $
$\displaystyle \log _{ \frac { 2 }{ 3 }  }{ \frac { 2 }{ 3 }  } >\log _{ \frac { 2 }{ 3 }  }{ \frac { 5 }{ 6 }  } >\log _{ \frac { 2 }{ 3 }  }{ 1 } $  (Since the base $\displaystyle \frac { 2 }{ 3 } <1)$
$\displaystyle \Rightarrow 1>\log _{ \frac { 2 }{ 3 }  }{ \frac { 5 }{ 6 }  } >0$

Multiple choice logarithm and its uses basic mathematical concepts physics

If $x=\log _{ a }{ bc } ,y=\log _{ b }{ ca } ,z=\log _{ c }{ ab } $, then the value of $\dfrac { 1 }{ 1+x } +\dfrac { 1 }{ 1+y } +\dfrac { 1 }{ 1+z } $ will be

  1. $x+y+z$
  2. $1$
  3. $ab+bc+ca$
  4. $abc$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Now, $1+x=\log _{ a }{ a } +\log _{ a }{ bc } =\log _{ a }{ abc } $
$\Rightarrow \dfrac { 1 }{ 1+x } =\log _{ abc }{ a } $
Similarly, $\dfrac { 1 }{ 1+y } =\log _{ abc }{ b } $ and $\dfrac { 1 }{ 1+z } =\log _{ abc }{ c } $
$\therefore \dfrac { 1 }{ 1+x } +\dfrac { 1 }{ 1+y } +\dfrac { 1 }{ 1+z } $
                    $=\log _{ abc }{ a } +\log _{ abc }{ b } +\log _{ abc }{ c } $
                    $=\log _{ abc }{ abc } =1$

Multiple choice logarithm and its uses basic mathematical concepts physics

Calculate $x$, to the nearest tenth: $\log _{12} 640 = x$

  1. $1.7$
  2. $2.6$
  3. $2.8$
  4. $53.3$
  5. $7,680$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Given, $x= \log _{ 12 }{ 640 } $

$=\log _{ 12 }{ 144\times 4.44 } $
$=\log _{ 12 }{ 144 } +\log _{ 12 }{ 4.44 } $
$=2+\log _{ 12 }{ 4.44 }$
$= 2.6$

Multiple choice logarithm and its uses basic mathematical concepts physics

If $\displaystyle { log } _{ 5 }{ log } _{ 5 }{ log } _{ 2 }x=0$, then the value of $x$ is

  1. $32$
  2. $125$
  3. $625$
  4. $25$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Given, $\displaystyle { log } _{ 5 }{ log } _{ 5 }{ log } _{ 2 }x=0$
$\displaystyle \Rightarrow \quad { log } _{ 5 }{ log } _{ 2 }x=50$
$\displaystyle \Rightarrow \quad { log } _{ 5 }{ log } _{ 2 }x=1\Rightarrow { log } _{ 2 }x=5$
$\displaystyle \Rightarrow x={ 2 }^{ 5 }=32$

Multiple choice logarithm and its uses basic mathematical concepts physics

The value of $\log _{10} 0.0006024$ is equal to

  1. $\overline {3}.7979$
  2. $\overline {1}.9779$
  3. $\overline {4}.7799$
  4. $0.7279$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$\log _{10}0.0006024$

Characteristics$=-4$
For mantissa ,read from the table $6024.$
Mantissa$=7799$ 
Thus, $\log _{10}0.0006024=$ characteristics of $0.0006024+$ mantissa of $0.0006024$
$=-4+0.7799$
$=\bar4.7799$
Hence, C is the correct option.

Multiple choice logarithm and its uses basic mathematical concepts physics

Using logarithm table, determine the value of $\log _{10}0.5432$.

  1. $\overline {1}.7350$
  2. $\overline {2}.7350$
  3. $0.7350$
  4. $0.07350$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$\log _{10}0.5432$

Characteristics$=-1$
For mantissa ,read from the table $5432.$
Mantissa$=7350$ 
Thus, $\log _{10}0.5432=$ characteristics of $0.5432+$ mantissa of $0.5432$
$=-1+0.7350$
$=\bar1.7350$
Hence, A is the correct option.

Multiple choice logarithm and its uses basic mathematical concepts physics

Antilog of the number $( -8.654)$ is equal to

  1. $2.18\times 10^{-8}$
  2. $2.18\times 10^{-9}$
  3. $2.218\times 10^{-9}$
  4. $2.218\times 10^{-8}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
$(-8.654)=-8+(-0.654)$
$=-8+(-0.654)+1-1$
$=-9+(1-0.654)=-9+0.346$

Actual digits of 0.346 from the log table $=2.218$

$\therefore$ $ anti \log(-8.654)=2.218\times 10^{-9}$
Multiple choice logarithm and its uses basic mathematical concepts physics

The antilog of $\overline {1}.8840$is equal to

  1. $76.56$
  2. $\overline {1}.7656$
  3. $0.7656$
  4. $7.656$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Antilog $\bar1.8840$

Characteristics$=-1$
Value of $0.8840$ from antilog table $=7656$

Now number of zeroes after decimal will be $0.$
Antilog $\bar1.8840=0.7656$
Hence, C is the correct option.