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Binomial Theorem question

2002 · Shift 0 · Q106
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Binomial Theorem question

2002 · Shift 0 · Q106

JEE MainMathematicsBinomial TheoremMCQ+4 / −1
The positive integer just greater than (1+0.0001)10000{\left( {1 + 0.0001} \right)^{10000}}(1+0.0001)10000 is
  1. A
    4
  2. B
    5
  3. C
    2
  4. D
    3
View written solutionFree

Correct answer: D

  1. Let x=(1+0.0001)10000=(1+110000)10000.x=\left(1+0.0001\right)^{10000}=\left(1+\frac{1}{10000}\right)^{10000}.x=(1+0.0001)10000=(1+100001​)10000.

We need the positive integer just greater than xxx, i.e. the smallest integer greater than xxx.

  1. Compare xxx with the known limit: (1+1n)n<efor all positive integers n.\left(1+\frac{1}{n}\right)^n<e \quad \text{for all positive integers } n.(1+n1​)n<efor all positive integers n. So, x=(1+110000)10000<e.x=\left(1+\frac{1}{10000}\right)^{10000}<e.x=(1+100001​)10000<e. Since e≈2.71828<3,e\approx 2.71828<3,e≈2.71828<3, we get x<3.x<3.x<3.

  2. Now show that x>2x>2x>2. Using the binomial theorem, (1+110000)10000=1+(100001)110000+(100002)1100002+⋯\left(1+\frac{1}{10000}\right)^{10000}=1+\binom{10000}{1}\frac{1}{10000}+\binom{10000}{2}\frac{1}{10000^2}+\cdots(1+100001​)10000=1+(110000​)100001​+(210000​)1000021​+⋯ The first two terms give 1+(100001)110000=1+10000⋅110000=2.1+\binom{10000}{1}\frac{1}{10000}=1+10000\cdot \frac{1}{10000}=2.1+(110000​)100001​=1+10000⋅100001​=2. All remaining terms are positive, hence x>2.x>2.x>2.

  3. Therefore, 2<x<3.2<x<3.2<x<3. So the smallest integer greater than xxx is 3.3.3.

  4. Checking options:

  • A: 444 — incorrect
  • B: 555 — incorrect
  • C: 222 — incorrect, since number is greater than 222
  • D: 333 — correct

Hence the correct answer is D.

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