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Quantitative Aptitude

LOGARITHM MCQs

Logarithms

Total Questions : 289 | Page 11 of 29 pages
Question 101.

If log 3 = 0.477 and `(1000)^x` = 3,  then `x` equals  :


  1.    0.0159
  2.    0.0477
  3.    0.159
  4.    10
 Discuss Question
Answer: Option C. -> 0.159

`(1000)^x  = 3`

`rArr  log[(1000)^x] = log 3`

`rArr  x log 1000 =  log 3`

`rArr  x log(10^3) = log 3`

`rArr  3 x log 10 =  log 3`

`rArr   3x = log 3        rArr   x = 0.477/3     = 0.159.`


Question 102.

If `log_10 2 = 0.3010, ` the value of `log_10 80` is :


  1.    1.6020
  2.    1.9030
  3.    3.9030
  4.    None of these
 Discuss Question
Answer: Option B. -> 1.9030

`log_10 80` = `log_10 (8 xx 10)`

=`log_10 8 + log_10 10`

=` log_10 (2^3) + 1`

=`3 log _10 2 + 1`

= (3 x 0.3010 + 1) = 1.9030.


Question 103.

If `log_10 2 = 0.3010` , the value of `log_10 5` is


  1.    0.3241
  2.    0.6911
  3.    0.6990
  4.    0.7525
 Discuss Question
Answer: Option C. -> 0.6990

`log_10 5  = log_10  (10/2)`

=` log_10 10 - log_10 2`

=`1 - log_10 2`

= (1 - 0.3010 ) =0. 6990



Question 104.

If `log_10 2 = 0.3010, ` Then  `log_2 10 ` is equal to  :


  1.    `699/301`
  2.    `1000/301`
  3.    0.3010
  4.    0.6990
 Discuss Question
Answer: Option B. -> `1000/301`

`log_2 10` =  `(1)/(log_10 2)`

= `1/03010` = `10000/3010`

=` 1000/301`


Question 105.

If log 27 = 1.431, then the value of log 9 is :


  1.    0.934
  2.    0.945
  3.    0.954
  4.    0.958
 Discuss Question
Answer: Option C. -> 0.954

Log 27 = 1.431.

`rArr   log(3^3) = 1.431 `        `rArr  3 log 3 = 1.431`

`rArr   log 3 = 0.477`

`:.`      log 9 = `log(3^2)` = 2 log3 = (2 x 0.477) = 0.954




Question 106.

If  `a = b^x , b = c^y and c = a^z,`  then the value of ` xyz`  is equal to :


  1.    - 1
  2.    0
  3.    1
  4.    abc
 Discuss Question
Answer: Option C. -> 1

`a = b^x , b = c^y , c = a^z `

`rArr  x = log_b a, y = log_c b , z = log_a c`

`rArr    xyz = (log_b a) xx (log_c b) xx (log_a c)`

`rArr     xyz = ((log a)/(log b) xx (log b)/(log c) xx (log c)/(log a))` = 1



Question 107.

If `log_10 7 = a,`  then `log_10 (1/70)` is equal to :


  1.    - (a + 1)
  2.    `(1 + a)^-1`
  3.    `a/10`
  4.    `(1)/(10a)`
 Discuss Question
Answer: Option A. -> - (a + 1)

`log_10 (1/70)`

=`log_10 1 - log_10 70`

=`log_10 (7 xx 10)`

=` - (log_10 7 + log _10 10`

= - (a + 1)



Question 108.

The value of `[ (1)/(log_((p//q)) x) + (1)/(log_((q//r)) x) + (1)/(log_((r//p)) x)]` is  :


  1.    0
  2.    1
  3.    2
  4.    3
 Discuss Question
Answer: Option A. -> 0

Given expression = `log_x (p/q) + log_x (q/r) + log_x (r/p)`

=`log_x (p/q xx q/r xx r/p)`

=`log_x 1 = 0`.


Question 109.

[ log `((a^2)/(bc))` + log `((b^2)/(ac))` + log `((c^2)/(ab))`] is equal to :


  1.    0
  2.    2
  3.    3
  4.    abc
 Discuss Question
Answer: Option A. -> 0

Given expression = log`((a^2)/(bc) xx (b^2)/(ac) xx (c^2)/(ab))`

= log1 = 0



Question 110.

`[ (1)/((log_a bc) + 1) + (1)/((log_b ca) + 1) + (1)/((log_c ab) + 1)]`  is equal  to :


  1.    1
  2.    `3/2`
  3.    2
  4.    3
 Discuss Question
Answer: Option A. -> 1

Given expression 

= `(1)/(log_a bc + log_a a) + (1)/(log_b ca + log_b b) + (1)/(log_c ab + log_c c)`

=`(1)/(log_a (abc)` + `(1)/(log_b (abc)` +` (1)/(log_c (abc)`

=`log_(abc) a  + log _(abc) b + log_(abc)  c`

=`log_(abc) abc ` = 1



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