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What is the greatest integer less than or equal to

3 201 + 2 201 3 197 + 2 197 \large \dfrac{3^{201} + 2^{201}}{3^{197} + 2^{197}}

81 64 80 96 128

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2 solutions

Note that:

3 201 + 2 201 3 197 + 2 197 = 81 ( 3 197 ) + 16 ( 2 197 ) 3 197 + 2 197 < 81 ( 3 197 ) + 81 ( 2 197 ) 3 197 + 2 197 = 81 \dfrac {3^{201}+2^{201}}{3^{197}+2^{197}} = \dfrac {81(3^{197})+16(2^{197})}{3^{197}+2^{197}} < \dfrac {81(3^{197})+81(2^{197})}{3^{197}+2^{197}} = 81

And:

3 201 + 2 201 3 197 + 2 197 = 81 ( 3 197 ) + 16 ( 2 197 ) 3 197 + 2 197 = 80 ( 3 197 ) + 3 197 + 16 ( 2 197 ) 3 197 + 2 197 = 80 ( 3 197 ) + ( 2 + 1 ) 197 + 16 ( 2 197 ) 3 197 + 2 197 By binomial series expansion = 80 ( 3 197 ) + 2 197 + 197 ( 2 196 ) + + 16 ( 2 197 ) 3 197 + 2 197 = 80 ( 3 197 ) + 2 197 + 98.5 ( 2 197 ) + + 16 ( 2 197 ) 3 197 + 2 197 > 80 ( 3 197 ) + 80 ( 2 197 ) 3 197 + 2 197 = 80 \begin{aligned} \frac {3^{201}+2^{201}}{3^{197}+2^{197}} & = \frac {{\color{#3D99F6}81(3^{197})}+16(2^{197})}{3^{197}+2^{197}} \\ & = \frac {{\color{#3D99F6}80(3^{197}) + 3^{197}}+16(2^{197})}{3^{197}+2^{197}} \\ & = \frac {80(3^{197}) + {\color{#3D99F6}(2+1)^{197}}+16(2^{197})}{3^{197}+2^{197}} & \small \color{#3D99F6} \text{By binomial series expansion} \\ & = \frac {80(3^{197}) + {\color{#3D99F6}2^{197} + 197(2^{196})+ \cdots}+16(2^{197})}{3^{197}+2^{197}} \\ & = \frac {80(3^{197}) + {\color{#3D99F6}2^{197} + 98.5(2^{197})+ \cdots}+16(2^{197})}{3^{197}+2^{197}} \\ & > \frac {80(3^{197}) + 80(2^{197})}{3^{197}+2^{197}} = 80 \end{aligned}

Therefore, 80 < 3 201 + 2 201 3 197 + 2 197 < 81 80 < \dfrac {3^{201}+2^{201}}{3^{197}+2^{197}} < 81 3 201 + 2 201 3 197 + 2 197 = 80 \implies \left \lfloor \dfrac {3^{201}+2^{201}}{3^{197}+2^{197}} \right \rfloor = \boxed{80} .

3 201 + 2 201 3 197 + 2 197 3 ( 201 197 ) ( 3 2 ) 3 4 1 = 80 \large \color{#3D99F6} \dfrac{3^{201} + 2^{201}}{3^{197} + 2^{197}} \approx \color{#D61F06} 3^{(201 - 197)} - (3 - 2) \color{#20A900} \implies 3^4 - 1 = \boxed{ 80 }

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