Economics

E:  I need money for a field trip.

Me:  What field trip?  When?  Where is the permission slip?  Where are you going?

E:  Jesus.  I just need $20 to listen to some guy talk about cancer.  It's not like I'm going to buy cocaine with it.  I don't even know what the going rate for cocaine is.

Me:  Well, you are asking for money for a trip that I know nothing about.  Yes, I am gonna question you.  And $20 won't buy you coke.  Maybe crack.

E:  Is there a difference?

Me:  Well, crack is cheaper coke.  Like the Great Value brand of cocaine.

E:  Hey...you buy Great Value stuff all the time...

Me:  If I bought cocaine it would likely be crack.  That's just good economics there.