Quantitative Aptitude
LOGARITHM MCQs
Logarithms
`(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.`
`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.
`log_10 5 = log_10 (10/2)`
=` log_10 10 - log_10 2`
=`1 - log_10 2`
= (1 - 0.3010 ) =0. 6990
`log_2 10` = `(1)/(log_10 2)`
= `1/03010` = `10000/3010`
=` 1000/301`
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
`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
`log_10 (1/70)`
=`log_10 1 - log_10 70`
=`log_10 (7 xx 10)`
=` - (log_10 7 + log _10 10`
= - (a + 1)
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`.
Given expression = log`((a^2)/(bc) xx (b^2)/(ac) xx (c^2)/(ab))`
= log1 = 0
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