Simplify $\dfrac{16 \cdot 2^{n+1} - 4 \cdot 2^{n}}{16 \cdot 2^{n+2} - 2 \cdot 2^{n+2}}$.

Simplify $\dfrac{16 \cdot 2^{n+1} - 4 \cdot 2^{n}}{16 \cdot 2^{n+2} - 2 \cdot 2^{n+2}}$.
  1. $\dfrac{1}{4}$
  2. $\dfrac{1}{2}$
  3. $1$
  4. $2$

Solution

Numerator: $2^{n}(16 \cdot 2 - 4) = 2^{n}(32 - 4) = 28 \cdot 2^{n}$. Denominator: $2^{n+2}(16 - 2) = 4 \cdot 2^{n} \cdot 14 = 56 \cdot 2^{n}$. Ratio $= \dfrac{28}{56} = \dfrac{1}{2}$.

Asked in: IMO

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