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I am working through some set theory exercises, and am stuck with this one:

$A = \left \{ 2,4,6,7,11 \right \}$

Find the set S1:

$S1 = \left \{ (n+4): n \in A) \right \}$

Taking away 4 from each member, of the set I get:

$A = \left \{ -2,0,2,3,7 \right \}$

The applet tells me the answer is wrong, but I can't figure out how!

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What you wrote is the set $\{n:n+4\in A\}$. Do you see the difference with the original question? –  fedja Dec 31 '11 at 13:43
2  
Ahh. So, it infact should be: $A = \left \{ 6,8,10,11,15\right \}$ –  Ray Dec 31 '11 at 13:49
    
Yes, exactly : ) –  Matt N. Dec 31 '11 at 13:52
    
Note that the correct TeX for set membership is \in rather than \epsilon. –  Henning Makholm Dec 31 '11 at 15:42
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1 Answer

up vote 3 down vote accepted

I think you don't want to take away $4$ but you want to add $4$:

$$ S_1 = \{ n + 4 \mid n \in \{ 2,4,6,7,11\} \} = \{ 2 + 4, 4 + 4, 6 + 4, 7 + 4, 11 + 4\} = \{ 6, 8, 10, 11, 15\}$$

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