Logarithms Practice Test 1

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Question : 9 of 40

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A solution of

\log_10 (x + 20) + \log_10 100= 5

is:

x = 900
x = 980
x = 1000
x = 920

Solution:

\log_10 (x + 20) + \log_10 100= 5

⇒\log_10 (x + 20) + \log_10 10^2= 5

⇒\log_10 (x + 20) + 2\log_10 10 = 5

⇒\log_10 (x + 20) + 2 = 5

⇒\log_10 (x + 20) =3

⇒x+20=10^3

x=1000-20=980

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