# Aptitude - Logarithm - Discussion

Discussion Forum : Logarithm - General Questions (Q.No. 9)
9.
If log10 5 + log10 (5x + 1) = log10 (x + 5) + 1, then x is equal to:
1
3
5
10
Explanation:

log10 5 + log10 (5x + 1) = log10 (x + 5) + 1

log10 5 + log10 (5x + 1) = log10 (x + 5) + log10 10

log10 [5 (5x + 1)] = log10 [10(x + 5)]

5(5x + 1) = 10(x + 5)

5x + 1 = 2x + 10

3x = 9

x = 3.

Discussion:
14 comments Page 1 of 2.

Gilbert Langat said:   2 years ago
@All.

According to me;
Log 5(4t+7) - log5t = 2.

Vijju said:   4 years ago
@Chi.

How log 10 10 = 1?

Chi said:   4 years ago
One of the laws of the log is log10 10=1
log2 2=1
log5 5=1
logx x=1

@Saim.

Log 2 to the power 2 (written as log 2^2) = 2*Log2 and not 1.

Victor said:   4 years ago
@Saim.

We can't replace it with log2^2 because log2^2 =2log2 not 1.

Devota said:   4 years ago
I'm not getting this, please anyone explain in detail.

Biswa said:   5 years ago
I want to all formula & explanation about logarithms?

Saim said:   6 years ago
It's solved wrongly. Because log2^2 or log4^4 is also equal to 1. If we put these in replace of one the answer is wrong.

Correct me, if I am wrong.

Ashmi said:   7 years ago
How logx x=1?

Sharmi said:   7 years ago
Logx x =1 (it's one of the property).
So, log10 10=1.
Inorder to find x, 1 is being replaced with log10 10.

Bhavya said:   7 years ago
Log10 10=1 so place of1 they take log10 10.