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There are 30 people in my math class. 12 of them have cool dads, 15 of them have cool moms, and 9 of them have cool dads and cool moms. How many people have moms and dads who are both uncool?

 Apr 6, 2020
 #1
avatar+20967 
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30 set of parents

 

9 sets of both cool dads and cool moms

 

12 have cool dads

     --  subtract out the 9 that also have cool moms and you get 3 cool dads that aren't married to cool

            moms

 

15 have cool moms

     -- subtract out the 9 that also have cool dads and you get 6 cool moms that aren't married to cool dads

 

9 have both cool dads and cool moms

3 have cool dads but uncool moms

6 have cool moms but uncool dads

This leaves 30 - 9 - 3 - 6  =  12 that have both uncool moms and uncool dads

 Apr 6, 2020
 #2
avatar+252 
0

I have a maybe simpler method:

Add the amount of people with cool parents(27) and subtract the number of people with both(9) to get 18 people with cool parents and 12 people have no cool parents

smileysmileysmiley

 Apr 6, 2020

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