Do you know the power of 1000?

Calculus Level 1

What is the smallest integer that is greater than ( 1 + 0.0001 ) 1000 (1 + 0.0001)^{1000} ?

Note: please don't use calculators, there are better ways to do this.


The answer is 2.

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10 solutions

Dieuler Oliveira
Jan 31, 2015

By using the Binomial Approximation , we know:

( 1 + b ) n 1 + n b (1 + b)^n \approx 1+nb , then:

( 1 + 0.0001 ) 1000 1 + 0.0001 × 1000 = 1.1 < 2 (1 + 0.0001)^{1000} \approx 1+0.0001 \times 1000 = 1.1 < 2

this rule not satify all problem.

Cymon Joshi - 4 years, 11 months ago
Jakub Šafin
Jan 5, 2015

We know that ( 1 + 1 0 4 ) 1 0 4 e (1+10^{-4})^{10^4} \approx e , so ( 1 + 0.0001 ) 1000 e 0.1 (1+0.0001)^{1000} \approx e^{0.1} . Since e e is slightly less than 3, e \sqrt{e} must be less than 2 already; e 0.1 e^{0.1} is even smaller, and obviously greater than 1, so the answer is 2.

Curtis Clement
Dec 29, 2014

Suppose that you don't have a calculator to hand. We must create a range for the value given. Firstly we will expand the bracket, using the Binomial Theorem (note that 0.0001 = 1 1 0 4 \frac{1}{10^4} ): ( 1 + 0.0001 ) 1000 (1+0.0001)^{1000} = 1 + ( 1000 1 ) {1000\choose1} . 1 1 0 4 \frac{1}{10^4} + ( 1000 2 ) {1000\choose2} . 1 1 0 8 \frac{1}{10^8} +...+ 1 1 0 4 000 \frac{1}{10^4000} . Now this is m o r e {more} t h a n {than} 1 + 1 1 0 4 \frac{1}{10^4} + 1 1 0 8 \frac{1}{10^8} +... = i = 0 \displaystyle \sum_{i=0}^\infty 1 1 0 4 \frac{1}{10^4} = 10000 9999 \frac{10000}{9999} . It is also l e s s {less} t h a n {than} : i = 0 \displaystyle \sum_{i=0}^\infty 1 1 0 i \frac{1}{10^i} = 10 9 \frac{10}{9} . In other words: 10000 9999 \frac{10000}{9999} < ( 1 + 0.0001 ) 1000 (1+0.0001)^{1000} < 10 9 \frac{10}{9} , so the next integer is 2 \boxed{2} .

Harsha K
Jan 31, 2015

1 to the power nearly anything is 1. So is any number closing in around 1. 1+0.0001 gives you 1.0001^1000. Which would be around 1.00000000000000000000.........00011. The integer after this number is 2.

Moderator note:

This is not true, a simple counterexample is: 1.0000 1 1000000 1.00001^{1000000} which is already larger than 20000 20000 . That fallacy that you made is that the small gradual increase of a number x x percentage wise cannot never exceed x + 1 x+1 .

That actually isn't true Any number bigger than 1 raised to a high enough power eventually grows to infinity. For example 1.0001^1000 is around 1.15

Seth Christman - 6 years, 4 months ago
Harish Nandan
Feb 18, 2016

f(x+∆x)=f(x)+f'(x)*∆x when ∆x->0. Taking f(x)=x^1000 and ∆x=0.0001 we get f(1.0001)=1.1 .Thus the answer is 2.

Aditya Paul
Feb 21, 2015

System.out.println ( Math.ceil (Math.pow (1.0001,1000) ) ) ;

I used this computer program in java, just one small line does the work, no need for binomial approximation or range calculation needed.

Moderator note:

Try not to use the help of computational assistance when one isn't required.

Michael Yi
Dec 29, 2014

Using the basics of the binomial theorem, we can see that the expression (1 + 0.0001)^1000 will be equal to:

(1^1000 * 0.0001^0) + (1^999 * 0.0001^1) + (1^998 * 0.0001^2) ... + (1^0 * 0.0001^1000)

The first term of each expression is simply 1, so we can "factor out" the 1 to make the new expression:

1(0.0001^0 + 0.0001^1 + 0.0001^2 + ... + 0.0001^1000)

We can easily see that besides the first number 0.0001^0, which is 1, the rest of the numbers will be extremely small approaching closer and closer to 0. Thus, the rest of the numbers are irrelevent except in showing us that they sum to be a number slightly greater than 0 but definitely less than 1.

1(1 + very small number) = 1.0001 with the 0001 repeating. The smallest positive integer greater than that expression is simply 2.

Luke Zhang
Feb 10, 2015

1+1000*0.0001=1.1 hence 2

Moderator note:

Your solution is marked wrong for obvious reasons. ( 1 + a ) b = 1 + a b (1+a)^b = 1 + a b is not an algebraic identity. Furthermore, you should mention you're using binomial approximation and you must specify the error term.

Sagar Majumdar
Jan 31, 2015

By binomial approximation- (1+x)^n=1+nx, when |x|<1. so, (1+0.0001)^1000 =1+(1000)(0.0001) =1.1 Therefore the required solution is 2.

Moderator note:

It should be ( 1 + x ) n 1 + n x (1+x)^n \approx 1 + nx .

George Harper
Dec 29, 2014

An easy way to think of this is to compare it to what happens if you multiply a number, say 1, by 1.01. It becomes 1.01 - or increases by 10%. In this case, we are multiplying 1 by 1.0001 (a 0.1% increase) 1000 times (if you count adding 0.0001 to 1 as being equivalent, which it is)... if you apply a 0.1% increase 1000 times you end up with a 100% increase. The number which is 100% greater than 1 is 2.

Moderator note:

Your use of percentage is wrong. "In this case, we are multiplying 1 by 1.0001 (a 0.1% increase)", it should be a 0.01% increase. And your logic is wrong. If you increase 1 1 by 0.01 % 0.01 \% for a thousand times, you won't get exactly 2 2 as the answer. What you're implying is that 1.000 1 1000 = 2 1.0001^{1000} = 2 or ( 10001 10000 ) 1000 = 2 \left ( \frac {10001}{10000} \right )^{1000} = 2 , multiplying both sides by 1000 0 1000 10000^{1000} shows an odd number equals to an even number which is a contradiction.

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