Math

What’s a Sadness Gap, You Ask?

I almost don't even want to tell you if you're studying for the SAT, because you really shouldn't worry your pretty little head about this.

They're rare -- in fact, so rare that I couldn't even find a single one in the entire Blue Book.  Not one.

UPDATE: Ok, one.  Stacey Howe-Lott found one in the Blue Book: Test 1, Section 7, Question 7 on page 415.

So what is a "sadness gap?"

It's officially known as the "Triangle Inequality Theorem," though when I heard it referred to as a "sadness gap" in PWNtheSAT's SAT Math Guide Beta Access, I thought, huh, how apropos. I've shed tears over this triangle question. In fact, I believe I gave up on math entirely in the 10th grade because of this "theorem."

When I say I've spent hours pouring over SAT books 30 years later in an attempt to finally understand this theorem in a way that will stick for more than a minute, I am not exaggerating.

Ok, here it is, Sadness Gap Explanation:

The basic thrust is this: if one side were longer than the sum of the other two, then how would those two shorter ones connect to form the triangle? They couldn't. And if one side was equal to the sum of the other two, would you have a triangle? No, you'd just have a straight line.

To drive this home: imagine your forearms (apologies to my armless friends) are two sides of a triangle, and the imaginary line that connects your elbows is the third side. If you touch your fingertips together and pull your elbows apart, eventually your fingertips have to disconnect...that's when the length between your elbows is longer than the sum of the lengths of your forearms. Neat, huh?

Do you get it?

I do.  For a second.  And then I don't.  But I will.  Because I want my 800.  And they could serve one up.  In fact, I've heard they have (though have yet to verify with my own eyes).*

Now go have fun, unless you want an 800.  And then it's better to be safe than sorry, but I feel your pain.

And if you haven't ordered PWNtheSAT's SAT Math Guide Beta Access, do it.  It's got the funny, which makes "sadness gaps" much more bearable.

And, it's filled with gems like this, The Pythagorean Triple.....

......which I can verify, having just finished all Blue Book triangle problems today, are prevalent.

*UPDATE: No sooner than I wrote that I hadn't seen a Sadness Gap with my own two eyes, then I saw one with my own two eyes:

I'm sort of surprised this is a #10.  Feels like a #19 to me.

Illustrations by Jennifer Orkin Lewis

 
  • http://blog.pwnthesat.com PWN the SAT

    What a beautiful sadness gap!

    I doubt anyone's going to misinterpret, but in reading this on your site I realize that the first sentence of the explanation should say " ...if one side were longer than the SUM OF THE other two..."

    • http://www.perfectscoreproject.com Debbie Stier

      Fixed.  It is a beautiful little sadness gap, isn't it?  (thanks to @augustwren:twitter )

      • Elise

        HAHAHA!  I was just reading this and after reading PWN the SAT's comment I went back and looked again because I had realized something was wrong with it and then I seemed to blink and it was suddenly fixed...it's too early in the morning to be confusing me that way!

        • http://www.perfectscoreproject.com Debbie Stier

          See, this is why I STILL need to work on it.  I didn't even notice that something was wrong.  Thank goodness for the world full of people help me fix my mistakes!

          • Elise

            To be fair, I hadn't really been sure what exactly was wrong with it and after I read more I understood it so I just had assumed that I had not understood the first part...but then I read the comment so I had gone back to look.  I'm not quite that smart...

            Also, I just wanted to tell you a funny thing that my daughter said yesterday.  Remember when you were writing that you were told that if you "feel" that a sentence needs a pause, add a comma (I was also told the same thing).  Well, my daughter told me yesterday that her teacher said that "sometimes adding a comma is a stylistic decision"  Ha ha ha!  I don't really know why this seems so funny to me...she didn't think it was funny at all.

          • http://www.perfectscoreproject.com Debbie Stier

            oh no!  This myth is going to become a reality.

            You have to get her Erica's book.  http://www.amazon.com/Ultimate-Guide-SAT-Grammar/dp/1463599889/ref=sr_1_1?ie=UTF8&qid=1313752733&sr=8-1

            Actually, you should get that book for her teacher.  

          • Elise

            Well, this teacher is a good teacher and I guess the key word in what he said is "sometimes".  He did teach her all the grammar rules as well.  In fact, she also was rambling on about dangling modifiers and since I am NOT studying for the SAT, my eyes glazed over.  She also told me he was very big on style and being creative.  Unfortunately, he left to go get his doctorate in California...but is keeping in touch by email with his students and has been proofreading essays for some of their summer work they have to do for other teachers!  He is quite dedicated.

          • http://www.perfectscoreproject.com Debbie Stier

            well that's encouraging.

  • Pckeller

    I don't want to increase the sadness...but alas, this one is not about the triangle inequality.  You don't ever need to find the third side to answer this.  Instead, think of the side that is 10 units long as the base and lay it down on a table.  Imagine there is a hinge connecting that piece to the piece that has length 7.  Since area = 1/2 base times height, to get the biggest possible area you need the biggest possible height.  How do you get that?  Adjust the hinge until the two sides are perpendicular!  That's all I'm saying for now...

    That said, I'm pretty sure I can find a couple in the blue book.  I'll look later and post if I find any..

    • http://blog.pwnthesat.com PWN the SAT

      I dig the hinge explanation. Right on.

      • Anonymous

        I like your arm/armless explanation (haven't yet got to that chapter in your book)

        I use keller's drawbridge rule, but I draw it out like a river and make students cut and paste the lengths of the bridge to span it.  Turning it into a concrete problem and talking about how they'll drown if the bridge is too short ( or flat) tends to make it stick.  Thus why I call this problem type the drowning triangle.

        • Pckeller

          When I am teaching this, I grab three pencils/crayons/whatever where two are really short compared to the third and I ask my students to connect them at their ends to build a triangle.  I tell them  it's like a physics lab.  That way, they are used to things not working!  They tell me (just like they do in physics lab):  "Mr Keller, It's not working. Can you help?"  But of course, I can't help!  If the two sides don't add up to more than the third, NO ONE can build the triangle.

    • Anonymous

      I found one triangle sides inequality in my database - Test 1, Section 7, Question 7 on page 415.
      Two sides of a triangle each have length 5. All of the following could be the length of the third side EXCEPT
      A. 1
      B. 3
      C. 4
      D. square root of 50
      E. 10

      • Pckeller

        Yes.  But I couldn't find another in the blue book.  And yet I KNOW I have seen a handful of these in the past, and I only use College Board tests.  I don't remember if they were on a QAS tests or maybe old PSATs but I do feel that this isolated factoid is worth knowing on the SAT -- useful but certainly not critical.  (Nowhere near as important as say functions or the angle rules.)  
         

        • http://blog.pwnthesat.com PWN the SAT

          Yeah...they're definitely out there. Just not very well represented in the Blue Book. 

          • http://www.perfectscoreproject.com Debbie Stier

            Equal rights for the sadness gaps.

          • Erik

            The 3rd side rule questions appear at a rate of about one per three SATs, based on past QAS tests. If you happen to have the tests, here they are: 10/06 Sec7 Q7, 10/09 Sec9 Q9, 5/06 Sec3 Q8, 1/10 Sec3 Q20, 10/10 Sec6 Q16.

          • http://www.perfectscoreproject.com Debbie Stier

            Thank you!

          • Erik

            The 3rd side rule questions appear at a rate of about one per three SATs, based on past QAS tests. If you happen to have the tests, here they are: 10/06 Sec7 Q7, 10/09 Sec9 Q9, 5/06 Sec3 Q8, 1/10 Sec3 Q20, 10/10 Sec6 Q16.

        • http://www.perfectscoreproject.com Debbie Stier

          Angle rules are my specialty.  I'd take 20 angle rules over 1 sadness gap....and 50 angle rules over 1 nested function.

      • http://www.perfectscoreproject.com Debbie Stier

        oh, ok,  Good catch.  I was following that database of math problems that someone forwarded me the link of.  Adding this one to list now.  

    • http://www.perfectscoreproject.com Debbie Stier

      Well, you know, I spent a long time thinking about this one -- and whether or not it falls into the sadness gap zone (PWN said no, and I believe was trying to explain thing you're saying above to me -- I think) -- but I also *think* (wouldn't swear by it) that I still need sadness gap understanding to get to the bottom of this (in my head anyway), even if there is another way to solve it.

      Starting w/E) 140=1/2bh   then 280 = bh  The third side needs to be less than 16 (i.e. sum of 7+10) to work, no?  which it doesn't for E.  Nor does it for D -- making C the largest sum.

      Am I making sense? (I barely am to myself)

      • http://blog.pwnthesat.com PWN the SAT

        You mean something like this?
        http://imgur.com/X9lEG

        Forgive my awful handwriting and photography skills. I may be doing more harm than good. :)

        • http://www.perfectscoreproject.com Debbie Stier

          haha.  Yes, just like that.  Printing out your lovely handwritten explanation now.

        • anotherSATmom

          This is a lovely explanation because it not only explains what you need to know but also loops through the answer options to find the right choice. The factoid you need to know is that the biggest triangle (by area) for any two sides (that don't have to be the hypotenuse), is always a right triangle. Is that as clear as mud? If you knew that, you'd go right to the answer...

          • http://www.perfectscoreproject.com Debbie Stier

            Nothing's as clear as mud to me at this moment in time.  My brain is saying "no more today...."

            Will try again to understand tomorrow....

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