## Miyuki 3 years ago Discrete Math Structure --> Set Operation. I asked in a previous question what is the "c" in c(A), and @tamtoan answered that it is for count. I was able to figure out the first question, but can't get the correct answer for the second question. The second question is: If c(A Union B) = 17, c(A Intersect B) = 3, and c(A) = c(B), then c(A) = ____? So, intersection is 3. Union is 17, which means, c(A) and c(B) should have 7 each right? I entered 7, but the result shows it up as incorrect. Did I make a silly mistake somewhere? >_< Thank you.

1. tamtoan

it's not 7 each :)...if 7 each in both A and B..you will get at most 14 for the union :)...remember union is 17 and that is less than count of A + count of B ...try drawing some pair of circles ..with intersection 3 first...and distribute other elements so that you can have a union of 17...i think you can figure it out :) if not, can check with me again..i think i got this

2. ajprincess

|dw:1348987956230:dw| May be u can this formula

3. ajprincess

*use

4. Miyuki

I got the answer after @tamtoan's explanation. Thank you! Thank you @ajprincee's as well, the equation is extremely helpful! :D I wish I could pick two best responses >.< I really appreciate the help!

5. ajprincess

That's k:) I think @tamtoan deserves the best response than me:)

6. tamtoan

It's great that you figure it out. Hope that you do well in the future. Thanks for the formular too ajprincess :)

7. ajprincess

yw:) @tamtoan