More Questions from Logarithm

If log โก 10 5 + log โก 10 ( 5 ๐‘ฅ + 1 ) = log โก 10 ( ๐‘ฅ + 5 ) + 1 log 10 โ€‹ 5+log 10 โ€‹ (5x+1)=log 10 โ€‹ (x+5)+1, find ๐‘ฅ x.

Aptitude Logarithm Difficulty: Medium
Choose an option
  • A
    2
  • B
    3
  • C
    4
  • D
    5

Answer

Correct Answer: 3

Explanation

Given data & domain

  • 5x+1 > 0, x+5 > 0 (log arguments must be positive).

Concept / Approach

  • Use log properties: log โก ๐‘Ž + log โก ๐‘ = log โก ( ๐‘Ž ๐‘ ) loga+logb=log(ab) and 1 = log โก 10 10 1=log 10 โ€‹ 10.

Step-by-step calculation log โก 10 [ 5 ( 5 ๐‘ฅ + 1 ) ] = log โก 10 [ 10 ( ๐‘ฅ + 5 ) ] log 10 โ€‹ [5(5x+1)]=log 10 โ€‹ [10(x+5)] โ‡’ 25 ๐‘ฅ + 5 = 10 ๐‘ฅ + 50 โ‡’25x+5=10x+50 15 ๐‘ฅ = 45 โ‡’ ๐‘ฅ = < ๐‘š ๐‘Ž ๐‘Ÿ ๐‘˜ > 3 < / ๐‘š ๐‘Ž ๐‘Ÿ ๐‘˜ > 15x=45โ‡’x=3

Verification5x+1 = 16 > 0, x+5 = 8 > 0 valid. Substitute to check equality.

Final Answer3

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