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Using only four 4's and any symbol, how can you make 10?

 Jan 9, 2015

Best Answer 

 #6
avatar+808 
+5

Double factorial (aka semifactorial) is a mathematical operation in which one multiplies "every other" natural number up to a given number. A more precise definition is:

 

$$n!!=\prod \limits_{i=0}^{k}(n-2i)= n(n-2)(n-4)(n-6)...$$

Where k = (n/2) - 1 

 

 

Or read more on the "Double Factorial" Wikipedia web page :)

 Jan 10, 2015
 #1
avatar+808 
+5

How about: 

 

4 + √4 +√4 +√4

 

 

Technically speaking you've used two's since √x = 2√x

 Jan 9, 2015
 #2
avatar+100813 
+5

4/4+4/4+4/4+4/4+4/4+4/4+4/4+4/4+4/4+4/4=10

 Jan 9, 2015
 #3
avatar+808 
0

Eureka!

 

4!!+(4+4)/4

 

Where "!!" stands for double factorial.

 Jan 9, 2015
 #4
avatar+100813 
0

Hi Tetration

What does double factorial mean ?

 Jan 10, 2015
 #5
avatar+27837 
+5

How about (44 - 4)/4?

.

 Jan 10, 2015
 #6
avatar+808 
+5
Best Answer

Double factorial (aka semifactorial) is a mathematical operation in which one multiplies "every other" natural number up to a given number. A more precise definition is:

 

$$n!!=\prod \limits_{i=0}^{k}(n-2i)= n(n-2)(n-4)(n-6)...$$

Where k = (n/2) - 1 

 

 

Or read more on the "Double Factorial" Wikipedia web page :)

Tetration Jan 10, 2015
 #7
avatar+100813 
0

Thanks Tetration - I have never seen that before.   

 Jan 11, 2015

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