Integer chemistry

Integers, like molecules, are built from atoms. However there's only one element in the periodic table of maths, namely the number 1, and all other integers can be built from it. For example, there are several ways to build the number 6:

6 = 1 + 1 + 1 + 1 + 1 + 1 = ( 1 + 1 ) ( 1 + 1 ) + 1 + 1 = ( 1 + 1 ) ( 1 + 1 + 1 ) 6 = 1+1+1+1+1+1 \\ = (1+1)*(1+1)+1+1 \\ = (1+1)*(1+1+1)

We say the number 6 has complexity 5, because that's the cheapest (using the fewest ones) way it can be built. The allowed operations are addition, multiplication and brackets. It's not allowed to write two ones next to each other to make 11.

What's the complexity of the number 15?


The answer is 8.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

31 solutions

Abhishek Paul
Jan 30, 2014

Its obvious. Only those numbers n which are not prime can be written as a × b a \times b , where both a and b are not equal to 1(prime factors of n). Thus multiplication can be used to decrease the number of 1's required, as shown in the example of 6 in the question.

Thus, 15 = 3 × 5 15=3 \times 5 , will give least number of 1's. But 3 = 3 × 1 3=3 \times 1 and 5 = 5 × 1 5=5 \times 1 are themselves prime. Therefore, 3 requires 3 *1's, as addition 3 = 1 + 1 + 1 3=1+1+1 will give them least number of 1's, whereas multiplication increases number of 1's as 3 = ( 1 + 1 ) × 1 + 1 3=(1+1)\times 1+1 or 3 = 1 × 1 + 1 + 1 3=1 \times 1+1+1 , both give * 4 1's.

Similarly 5 = 1 + 1 + 1 + 1 + 1 5=1+1+1+1+1 requires *5 * 1's. Hence total number of 1's = 3 + 5 = 8 =3+5=\boxed{8} .

yes 8 is a crrct ans.

Anju Arora - 7 years, 3 months ago

yea true.

Arvind Krishna - 7 years, 3 months ago

yes it is 8

Kartikeyan Litlle Dhoni - 7 years, 1 month ago

8 of course..

math man - 6 years, 11 months ago
Upendra Singh
Jan 26, 2014

Find the prime factors of the number 15.

We find "prime" factors because they cannot further be reduced. So they can only be formed by addition of "1's" .

Moreover, this gives us the fewest no. of "1's" because these are the lowest possible numbers which can be multiplied to form the given number. Hence we get the lowest no. of "1's".

Here its 3 and 5.

So, 3x5=(1+1+1)x(1+1+1+1+1)=15

Total no. of "1's" used is 8 ANS

For complexity of 6, the shortest way is the prime fatcors= 3 * 2=(1+1+1) * (1+1). Similarly in the case of fifteen the prime factors are-3 * 5 or (1+1+1) * (1+1+1+1+1).Therefore it consists of 8 ones(1) and therefore the answer is 8.

Atul Saswat
Jan 26, 2014

15 is the product of 5 and 3 ...and it cant be simplified anymore as both of them are prime numbers yet..so 5's complexity is 5 and 3's is 3 .Adding them it sums to 8 , the answer. Easy stuff .all you got to do is to simplify it and try to find the maximum factors although i didn't need to do anything such here....

there are two solutions:

(1+1+1)x(1+1+1+1+1) and (1+1+1) x (((1+1) x (1+1))+1)

Andrés Charria - 7 years, 4 months ago
Abhinav Ankur
Mar 21, 2014

the only numbers by which 15 is divisible is 3 and 5. so adding 3 and 5 we get 8, which is the answer to the given question.

Ajith Gade
Jan 30, 2014

(1+1+1+1+1)(1+1+1)

Diyanko Bhowmik
Mar 30, 2014

Basically, if we factorize the number, we will get the product of the minimum numbers to make that number . . . So, when we factorize 15, we get it as 3*5 . . . so we will need 8 = (5+3) 1s.

Ramji Varadarajan
Mar 20, 2014

Since 6=(1+1+1)*(1+1),Hence 6 is a product of 3 and 2. Here the sum of 1's is 5.

Similarly, 15 is a product of 3 and 5, Hence 15=(1+1+1)*(1+1+1+1+1). Here the sum of 1's is 8.

Rabiul Islam
Mar 17, 2014

15= 3 5= (1 1 1) (1+1+1+1+1)

Syed Ali
Mar 12, 2014

(1+1+1+1+1)*(1+1+1) =5 * 3 =15 so complicity is 5+3=8

Rahul Gaur
Mar 7, 2014

15=(1+1+1)*(1+1+1+1+1)

Arvind Krishna
Feb 28, 2014

8 is the obvious answer because the only simple way to get 15 is either (5) (3) or (3) (5). So 5+3 is nothing but 8. So Ans=8.

Aakash Singh
Feb 21, 2014

3 5 (1+1+1) (1+1+1+1+1) = 15

Zafarali Ahmed
Feb 20, 2014

L e t 6 = 3 2 { a p r o d u c t o f p r i m e s } ( 1 + 1 + 1 ) ( 1 + 1 ) C o m p l e x i t y : 3 + 2 = 5 L e t 15 = 3 5 { a p r o d u c t o f p r i m e s } = ( 1 + 1 + 1 ) ( 1 + 1 + 1 + 1 + 1 ) C o m p l e x i t y : 3 + 5 = 8 n = a 1 a i { w h e r e a 1 . . . a i a r e p r i m e } C o m p l e x i t y : = a 1 + . . . + a i Let\quad 6\quad =\quad 3\quad *\quad 2\quad \{ a\quad product\quad of\quad primes\} \\ \qquad \qquad (1+1+1)\quad *\quad (1+1)\\ \therefore Complexity:\quad 3+2\quad =\quad 5\\ Let\quad 15\quad =\quad 3\quad *\quad 5\quad \{ a\quad product\quad of\quad primes\} \\ \qquad \qquad =(1+1+1)*(1+1+1+1+1)\\ \therefore Complexity:\quad 3+5\quad =\quad 8\\ \\ \Longrightarrow \quad n\quad =\quad a_{ 1 }*\cdots *a_{ i }\quad \{ where\quad a_{ 1 }...a_{ i }\quad are\quad prime\} \\ Complexity\quad :=\quad a_{ 1 }+...+a_{ i }

What is that Complexity

Matheswari selvaraj - 7 years, 2 months ago
Adithyan Shob
Feb 17, 2014

if we look closely 6=2*3

similarly 15 shlould be equaly to 3*5 as per given pattern it wil be

15=(1+1+1)*(1+1+1+1+1) hence complexity = 8

Sirisha Kethineni
Feb 12, 2014

(1+1+1)*(1+1+1+1+1)

15=(1+1+1)*(1+1+1+1+1)

so, the number 15 has complexity 1+1+1+1+1+1+1+1=8

Aqib Pandit
Feb 9, 2014

according to fundamental theorem of Arithmetics "Any integer greater than 1 is either a prime number, or can be written as a unique product of prime numbers (ignoring the order)".

(1+1+1) (1+1+1+1+1) which means 3 5=15 where 3,5 are primes and there is no way you can make 3 and 5 from any product combination

Mohammad Fiyaz
Feb 8, 2014

The complexity of number 15 is 8.

15 = (1 + 1 + 1) * (1 + 1 + 1 + 1 + 1)

Hitesh Pol
Feb 6, 2014

the complexity of number 15 can be written as 15=(1+1+1) (1+1+1+1+1)

Sidhi Kharkia
Feb 5, 2014

15 = 1+1+1+1+1+1+1+1+1+1+1+1+1+1+1

= (1+1+1) * (1+1+1+1+1)

so, we can say the no. 15 has complexity 8.

Absaar Shoaib
Feb 5, 2014

we break 15 into its prime factors by prime factorisation method. We get that there is no other way to get 15 than to multiply 3 with 15... 3 can be broken as (1+1+1) and 5 can be broken as (1+1+1+1+1) so we get the complexity 3ones + 5ones= 8

Bestin Thomas
Feb 3, 2014

for this we we can do it by finding the biggest 2 numbers and adding it in this case the number is 15 we can split it into 3*5 and adding it =3+5=8 we can check this by (1+1+1)(1+1+1+1+1)

Azhar Aslam
Feb 2, 2014

As number 6 has complexity 5 (1+1) (1+1+1) just like that 15 has complexity of 8 (1+1+1) (1+1+1+1+1)

Prasun Biswas
Feb 1, 2014

Well, I saw that the ways can be as follows :---

15 = 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 15=1+1+1+1+1+1+1+1+1+1+1+1+1+1+1

15 = ( 1 + 1 + 1 ) ( 1 + 1 + 1 + 1 + 1 ) = ( 1 + 1 + 1 + 1 + 1 ) ( 1 + 1 + 1 ) 15=(1+1+1)*(1+1+1+1+1)=(1+1+1+1+1)*(1+1+1) and,

15 = ( ( 1 + 1 ) ( 1 + 1 ) + 1 ) ( 1 + 1 + 1 ) 15=((1+1)*(1+1)+1)*(1+1+1) , etc.

Then, I counted number of 1's in each of the formations and saw that 15 can be created at the very least by using 8 1's. Actually, truth be told, I just used trial and error method to solve this.

Imran Haider
Feb 1, 2014

(1+1+1)*(1+1+1+1+1)

Saurav Jha
Jan 31, 2014

As you can see in the example they have given the complexity of 6 is 5 because it can be solved by using 5 ones, which is (3) (2) = (1+1+1) (1+1). similarly 15 = (3) (5) = (1+1+1) (1+1+1+1+1). as we know the lowest number of ones that we can use is only when the multiples of 15 will be multiplied. and then only you will get lowest value of complexity. so this is how we get complexity= 8 for 15.

Mohamed Adawy
Jan 31, 2014

(1+1+1)*(1+1+1+1+1)

Tanim Jaber
Jan 30, 2014

(1+1+1) * (1+1+1+1+1)

Saba Majeed
Jan 30, 2014

11=1+(1+1+1+1+1)*(1+1)

Neeraj Agrahari
Jan 30, 2014

number 6 is equal to minimum value of multiplier 2 and 3.2+3=5 same as case of 15 is equal to minimum value of multiplier 3 and 5 .3+5=8 so ans is 8

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...