Aptitude - Logarithm - Discussion

Discussion :: Logarithm - General Questions (Q.No.1)

1. 

Which of the following statements is not correct?

[A]. log10 10 = 1
[B]. log (2 + 3) = log (2 x 3)
[C]. log10 1 = 0
[D]. log (1 + 2 + 3) = log 1 + log 2 + log 3

Answer: Option B

Explanation:

(a) Since loga a = 1, so log10 10 = 1.

(b) log (2 + 3) = log 5 and log (2 x 3) = log 6 = log 2 + log 3

      log (2 + 3) log (2 x 3)

(c) Since loga 1 = 0, so log10 1 = 0.

(d) log (1 + 2 + 3) = log 6 = log (1 x 2 x 3) = log 1 + log 2 + log 3.

So, (b) is incorrect.


K.Manohar Reddy said: (May 22, 2011)  
Its absolutely correct.

Begum said: (Aug 21, 2011)  
Its great.

Venu said: (Oct 2, 2014)  
If they say log 6 = log 2 + log 3, then log (2+3) = log 2 + log 3.

Can someone explain ?

Vikash said: (Oct 20, 2014)  
log 6 = log(2*3) = log 2 + log 3.

But log(2+3) =log 5 which is not equal to log 6.
So, log(2+3) != log 2 + log 3.

Tendai said: (Jan 18, 2015)  
What about 243 base 9?

Akshayaa said: (Mar 19, 2015)  
What about 828 with base 2?

Murali said: (Jul 6, 2015)  
243 base 9.

This mainly 243 = 3*3*3*3*3 = 3^5.

And 9 = 3*3 = 3^2.

So answer is 5/2. I dot no how to write log in keyboard.

Palak Kapoor said: (Oct 1, 2015)  
If a=5 and b=4 then what is the value of log (a-b) (a^2-b^2-2^b)?

Shashi said: (Oct 4, 2015)  
Its awesome.

Ssd said: (Oct 13, 2015)  
What is log to the base 5 512?

Garvit said: (Jan 18, 2016)  
Option D can't be considered answer. It's tricky actually:

LHS:

log (1+2+3) = log 6. [1+2+3 = 6].

RHS:

log1 + log2 + log3 = log (1x2x3) = log 6.

Since LHS = RHS (no matter how it comes) D isn't the option.

Suhaas said: (May 1, 2016)  
@Palak Kapoor.

The answer is undefined.

log{5 - 4}[5^2 - 4^2 - 4]
log{1}[25 - 16 - 16]
log[25 - 32]
log[- 7]
log value for -ve is undefined.

Sylvester said: (Jun 13, 2016)  
The given answer is absolutely correct.

Meenakshi said: (Jul 19, 2016)  
The anwer is absolutely correct according to log properties.

It's log a + log b = log(a * b).
not log(a + b) = log(ab).

Ravi said: (Dec 3, 2016)  
@all.

B is absolutely correct.

Disha Jhan said: (Mar 11, 2017)  
The answer B is correct. I agree with it.

Isaac said: (Mar 14, 2017)  
Can someone help me understand how D is a true statement?

If log6=10^6=1,000,000
how is that equal to log1+log2+log3?
=10^1+10^2+10^3,
=10+100+1000,
=1110.

Sanyal said: (Mar 14, 2017)  
Correct, Thanks for the given explanation.

Dhaval said: (Nov 23, 2017)  
D is also incorrect.

log(1+2+3) = log 1* log 2 * log 3.

Riya Raj said: (Mar 15, 2018)  
I'm also confused because it both the cases results are coming the same soo however it's different. Please explain me.

Deepak said: (May 6, 2018)  
I am not understanding this. Can anyone explain by taking general variable?

Kity said: (Jun 14, 2018)  
How, Please explain this.

Abhishek said: (Aug 6, 2018)  
The answer B is correct. I agree with it.

Omkar Rajale said: (Aug 24, 2018)  
Please explain the option D.

Keerthana said: (Jan 31, 2019)  
Thanks all for explaining.

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