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View Full Version : Typo in Sklansky Column

10-19-2002, 04:03 PM

Mike Haven
10-19-2002, 05:07 PM
no

there are 17 boys (13 girls)

there may be, say, 2 redheaded boys, so of the 4 redheads 2 are girls

so there are 19 boys or redheads (in this case)

ronniejames
10-19-2002, 09:18 PM
You need to read more carefully. You'll notice that you consider that the answer might be 19. Sklansky writes: "To get the right answer, you would in fact have to subtract the number of redheaded boys from 17. See why?" There are two possible typos in the column. If the published "13 girls" was intended to be '13 boys', then everything else is correct. If, as you suggest, we are to subtract the 13 girls from a total of 30 children, giving us 17 boys, then the two places where the number 17 appears should read, 21. I do not, even for a moment, entertain the possibility that Sklansky gave the wrong answer. It's too simple and he's far too competent.

Mike Haven
10-20-2002, 06:55 PM
i didn't see his article

i gave an example to show that his instructions were correct

his instructions are correct:

"There are 30 children in your child's class. How many are either boys or redheads? If I tell you that there are 13 girls and four redheads, that doesn't mean the answer is 17...To get the right answer, you would in fact have to subtract the number of redheaded boys from 17."

if i tell you there are 13 girls in a class of 30 there are 17 boys

if i tell you there are 4 redheads they may be boys or girls

if there are, say, two redheaded boys then you have to subtract this number from the 17 boys = 15

otherwise you are double-counting the redheaded boys

ronniejames
10-21-2002, 03:29 AM

Mike Haven
10-21-2002, 04:09 AM
"To GET the right answer ..."

the calculations don't STOP at "... you would in fact have to subtract the number of redheaded boys from 17"

they INCLUDE that process

to make your ham and eggs you have to get a chicken first - well - maybe not - but you take the point?

ronniejames
10-21-2002, 04:17 AM
I'm afraid I have to throw in the towel. I just don't understand what you're driving at. It really isn't all that complicated. Really.

BruceZ
10-21-2002, 04:38 AM
There are 30 children in your child's class. How many are either boys or redheads? If I tell you that there are 13 girls and four redheads, that doesn't mean the answer is 17.

No, why would anyone think it is 17? One might naively think it is 21, since this is 17 boys + 4 readheads. But then you would have to subtract the redheaded boys from 21 not 17. Clearly this is a typo and both bold words above should be boys. Then you subtract redheaded boys from 17 to get the final answer. This is how the demonstration of the inclusion-exclusion principle should be done.

Mike Haven
10-21-2002, 09:08 AM
yep - it's a typo alright - i think it should be corrected to save anyone becoming confused

happyjaypee
10-21-2002, 06:32 PM

Skanlsky explanation would work whit the fellowing equation too:

Is thought process is just in the midlle of the explanation. I agree tought that it is confusing. I reed the post on CP and got a little lost. I Understanded it reading your posts

BruceZ
10-21-2002, 07:33 PM
True, but I'm sure it's a typo because of the suggestion that someone might incorrectly think the answer should be 17 (instead of 21). Just changing girls to boys causes everything else to make perfect sense.

10-22-2002, 02:18 PM
but what if one of the children who *isn't* a boy also *isn't* a girl. that happens sometimes, sadly. many corrections are needed to make this column make sense; Sklansky should make them before someone loses a bundle in a high stakes game

ronniejames
10-22-2002, 05:35 PM
In my original post, I attempted, in all innocence, to point out a typo in David Sklansky's most recent column. I never considered the possibility that I was instigating a debate---I mean, what is there to debate? Guys: this is not complicated stuff. Let's give it a rest.

Mike Haven
10-22-2002, 10:15 PM
lol! /forums/images/icons/grin.gif

we're just funning wid ya ronnie! /forums/images/icons/smirk.gif

ronniejames
10-23-2002, 06:38 PM
You guys had me worried. Mike, if you're ever in New York City, I'll buy you a pint of Guinness and introduce you to a fantastic Irish card magician at a pub called Cronin &amp; Phelan's.

Mike Haven
10-23-2002, 08:27 PM