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Question

What value should come in the place of question mark (?) in the following question:
$(12\times12)^3 \div (144\times12)^3 \times (20736)^2 = 12^?$

The correct answer is
5

Solving for the Unknown Exponent

The question requires finding the value of the exponent represented by the question mark (?) in the given equation:

$ (12\times12)^3 \div (144\times12)^3 \times (20736)^2 = 12^? $

To solve this, we need to simplify the left side of the equation using the laws of exponents, expressing each term as a power of 12.

Simplifying the Equation Components

  • First term: $ (12\times12)^3 = (12^2)^3 $. Using the power of a power rule $ (a^m)^n = a^{m \times n} $, this becomes $ 12^{2 \times 3} = 12^6 $.
  • Second term: $ (144\times12)^3 $. Since $ 144 = 12^2 $, the term is $ (12^2 \times 12^1)^3 $. Using the product of powers rule $ a^m \times a^n = a^{m+n} $, this simplifies to $ (12^{2+1})^3 = (12^3)^3 $. Applying the power of a power rule again gives $ 12^{3 \times 3} = 12^9 $.
  • Third term: $ (20736)^2 $. We need to express 20736 as a power of 12. $ 12^4 = 20736 $. So, the term is $ (12^4)^2 $. Using the power of a power rule, this becomes $ 12^{4 \times 2} = 12^8 $.

Applying Exponent Laws

Substitute the simplified terms back into the original equation:

$ 12^6 \div 12^9 \times 12^8 = 12^? $

Now, apply the division and multiplication rules for exponents:

  • Division: $ a^m \div a^n = a^{m-n} $. So, $ 12^6 \div 12^9 = 12^{6-9} = 12^{-3} $.
  • Multiplication: $ a^m \times a^n = a^{m+n} $. Applying this to the result: $ 12^{-3} \times 12^8 = 12^{-3+8} = 12^5 $.

Determining the Final Exponent

The simplified equation is:

$ 12^5 = 12^? $

By equating the exponents on both sides, we find:

$ ? = 5 $

Thus, the value that should come in place of the question mark is 5.

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Important Questions from Unit Digit

  1. The unit digit in 4 × 38 × 764 × 1256 is:

  2. How many times does the number 3 occur in unit's place for numbers ranging from 1 to 100?

    A. 20

    B. 11

    C. 10

    D. 19

  3. Find the unit digit in the given factor (3451) 51 × (531) 43 .

    A. 6

    B. 4

    C. 1

    D. 9

  4. What is the unit digit of 178 × 593 + 157?

  5. Find the unit digit of $(123)^{123} \times (347)^{347} \times (568)^{568}$.

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