Question of The Day06-04-2020

The series \(\frac{1}{1+\log 2}\),\(\frac{1}{1+\log 8}\),and \(\frac{1}{1+\log 32}\) are in

Answer

Correct Answer : c ) Harmonic progression

Explanation :

Quick Approach

For such a series if the terms inside the log are in Geometric progression then, the series will be in Harmonic progression.

Hence, (c) is the correct answer.

Basic Approach

Consider the given series

 \(\frac{1}{1+\log 2}\),\(\frac{1}{1+\log 8}\),and \(\frac{1}{1+\log 32}\) 

Here,

Inverse of the numbers of the series will be

\({1+\log 2}\), \({1+\log 8}\)\({1+\log 32}\)

Or,

\({1+\log 2}\), \({1+\log 2^{3}}\)\({1+\log 2^{5}}\)

\({1+\log 2}\), \({1+3\log 2}\)\({1+5\log 2}\)

Here,

2nd term – 1st term ⇒ \({1+3\log 2}\)– (\({1+\log 2}\)) = \({2\log 2}\)

Also,

3rd term – 2nd term ⇒\({1+5\log 2}\)– (\({1+3\log 2}\)) = \({2\log 2}\)

As, the common difference (d) of the series is the same

Thus, the inverse of the question series is an arithmetic progression.

And, therefore, the given series is a harmonic series.

Hence, (c) is the correct answer.

Such type of question is asked in various government exams like SSC CGL, SSC MTS, SSC CPO, SSC CHSL, RRB JE, RRB NTPC, RRB GROUP D, RRB OFFICER SCALE-I, IBPS PO, IBPS SO, RRB Office Assistant, IBPS Clerk, RBI Assistant, IBPS RRB OFFICER SCALE 2&3, UPSC CDS etc.

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