CAT Practice : Exponents and Logarithms

Basic Identities of Logarithms

Basic identities of Logarithm

    Q.10: If 33+6+9+………3x = (0.)-66, what is the value of x?
    1. 3
    2. 6
    3. 7
    4. 11


  • Correct Answer
    Choice D. 11

Detailed Solution

First of all, let us define the xth term.
33+6+9+……….3x = (0.)-66
Whenever you encounter a distinctive number such as one given in R.H.S of above equation, always try to find its significance in the context of question. In this case L.H.S has 3power, so (0.) must be some form of 3power.
With little hit and trial, you may find
33(1 + 2 + 3 + ...X) = 3 -3 * -66
=> 33*66

x(x+1) = 132
Solving this equation for x > 0, we get x= 11. You should directly be able to see that 132 = 11 x 12 =) x= 11
And avoid wasting time solving the complete equation.
Correct Answer is (D)

Correct Answer: 11

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More questions from Exponents and Logarithms

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