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Could you tell me the number of final zeros in the product of all the whole numbers between 100 and 200? I think the answers is 27 but I need some kind of external confirmation. thank you for your time

 Sep 18, 2017
 #1
avatar+1491 
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So are you asking for something like 200! but only to 100 and to determine the amount of zeros from the product?

 

c:

 Sep 18, 2017
 #2
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Yep. And 100 and 200 are both part of the product

 Sep 18, 2017
 #3
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Yes to be fair I calculated the number of zeros in 100! and 200! and then I did the difference adding the two zeros for 100

 Sep 18, 2017
 #4
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How did you calculate the number of zeros in 200! Do you know that there is a trick to find the number of trailing zero in ANY number, such as 10^12! ?

 Sep 18, 2017
 #5
avatar+124676 
+1

 

Number of zeroes from 100 to 200 [inclusive] =

 

Each multiple of "5"  from 100 to 200 adds an additional  "0"  =    20

 

Each multiple of 25 from 100 to 200  adds another "0"  =   4

 

Each multiple of 125 adds another  "0"  = 1

 

So.....  we have 2 "0s"  in 100  +  20  + 4 + 1   = 2 + 20 + 4 + 1   27

 

We  can confirm this by evaluating    200!  / 99!   here : https://www.wolframalpha.com/input/?i=200!+%2F99!

 

 

 

cool cool cool

 Sep 19, 2017
edited by CPhill  Sep 19, 2017

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