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FInd the largest prime that divides 27! + 28!.

 Jun 24, 2020
 #1
avatar+134 
+1

So you have to find the lagest prime number under 28, beacuse if you multiple 2 numbers, even if they are prime, you will get a compostie number. And we know that the largest prime number less than 28 is 23, so from here the answere is 23.

 Jun 24, 2020
 #2
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Since both have 27 factorial, we can factorize to get 27! (1+28) = 27! * 29. 

The largest prime that divides 27! + 28! is 29. 

 Jun 24, 2020
 #3
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I don't get were you get the 28+1

ItzMe  Jun 24, 2020
 #4
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28! means 28 factorial which is 28*27*26...*1. 

27! is 27*26*25...*1.

So we can take out 27!. 

thelizzybeth  Jun 24, 2020
 #5
avatar+134 
+1

Sorry, I just got it. My bad. Sorry.

ItzMe  Jun 24, 2020
 #6
avatar+307 
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No worries! :)

thelizzybeth  Jun 24, 2020

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