Wednesday, November 09, 2011

I really liked this one (the followup)

I recently wrote about an interesting question (not Oracle related!).  I found the question interesting because it reminds me of so many questions I actually receive about Oracle.  They are vague, incomplete, ambiguous, confusing at times.

The question I referred you to fell squarely in that category.  It was:
If you choose an answer to this question at random, what is the chance you will be correct?
a) 25%
b) 50%
c) 60%
d) 25%

They are missing the correct answer in the list!  And adding the correct answer would change the answer - so that it might be incorrect as well.  Meaning - there is more missing here than supplied.  You don't stand a chance of answering the question at all.

I put forth that the answer is "e) none of the above" - making the right answer "20%".

Looking at the problem, if you assume the right answer is 25% - because you have a 1 in 4 chance of selecting any one of the items - the probability you will get the right answer randomly is 50%.  So, it cannot be 25% - if it were - it would be 50% (confusing, yes).

Moreover, if you assume 50% is correct, then the right answer is 25% - because the chance of picking 50% is 1 in 4.

If you assume 60% is correct - well, I don't know what to say.

The question itself seems to somehow affect the answer - the act of answering the question changes the answer.  Sort of like when you run a program in the debugger and it works perfectly - but when you run it standalone it crashes (that has never happened to me, nope, not a chance...).

So, my answer is "e) none of the above"
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19 Comments:

Blogger Daniel said....

Hello Tom,

What about:

a) red
b) blue
c) brown
d) red

The terms are: choose, random, chance - and human mind walk to percent, statistics and again chance..

But the only chance you have "here" is / or could be "no chance".. any way.. beautiful question because of the beauty of mind..

Daniel

Wed Nov 09, 02:50:00 PM EST  

Anonymous Anonymous said....

Hi Tom,
a friend of mine pointed out that the headaches will start when you replace 60% with 0% :)

Thu Nov 10, 05:02:00 AM EST  

Blogger Thomas Kyte said....

@Anonymous

if you replace 60% with 0% then...

If 0% was correct, the odds would be 25%, but there are 2 25%'s so it would be 50%, but there is only 1 50% so it would be 25% and so on. Infinite loop ;)

Thu Nov 10, 06:18:00 AM EST  

Blogger Girl Next Door (gnd) said....

I'd like to think I have the most chances of getting it right, so I'll go with 60% (the largest)
;-)

Just kidding...

Thu Nov 10, 08:27:00 AM EST  

Anonymous Sokrates said....

... So, my answer is "e) none of the above"

I am quite surprised by that.
not "it depends" ? - I have the feeling that if you choose a question on asktom randomly, the chance that "it depends" is the correct answer is approximately 60%

Thu Nov 10, 09:15:00 AM EST  

Blogger George Joseph said....

This comment has been removed by the author.

Thu Nov 10, 11:19:00 PM EST  

Anonymous Andy C said....

That's what I thought - none of the above.

However, as the question asks "what is the chance?", not "what is the answer?".

If the actual answer is not on the list (yours isn't), then the "chance" of you picking it is 0%, surely?

Fri Nov 11, 04:10:00 AM EST  

Blogger Sheeri K. Cabral said....

"The question itself seems to somehow affect the answer - the act of answering the question changes the answer. "

Yep, it's Schrodinger's question!

Wed Nov 16, 06:08:00 AM EST  

Anonymous Erwin said....

Hi Tom,

You wrote "If you assume 60% is correct - well, I don't know what to say."

Most comments here are based on the assumption that "choose at random" implies that all answers have the same probability of being selected. Since that has not been stated in the question, in my opinion even "c) 60%" could be the right answer.

For example, you could "choose at random" by rolling a 20-sided die and pick answer "a) 25%" if the outcome is 1..2, "b) 50%" if it is 3..4, "c) 60%" if it is 5..16 and "d) 25%" if it is 17..20. When you follow this procedure, then 60% of the time, you will pick the answer "c) 60%".

Erwin.

Fri Nov 18, 11:34:00 AM EST  

Anonymous Anonymous said....

Why dont we just ask the oracle?

-- create the multiple choice table
SQL> create table stats (a varchar2(1),b number);

Table created.

SQL> insert into stats values ('a',25);

1 row created.

SQL> insert into stats values ('b',50);

1 row created.

SQL> insert into stats values ('c',60);

1 row created.

SQL> insert into stats values ('d',25);

1 row created.

SQL> commit;

Commit complete.

-- calculate the probabilities
SQL> select a,b, (count(*) over(partition by b) / count(*) over() *100) as probabilty_to_hit_b from stats;


A B PROBABILTY_TO_HIT_B
- ---------- -------------------
a 25 50
d 25 50
b 50 25
c 60 25

-- and now, dear oracle, tell us the correct answer
SQL> select a,b from
2 (select a,b, (count(*) over(partition by b) / count(*) over() *100) as probabilty_to_hit_b from stats)
3 where b=probabilty_to_hit_b;

no rows selected

-- oh well, the oracle stays silent .... let's replace 60% by 0% now...

SQL> update stats set b=0 where a='c';

1 row updated.

SQL> commit;

Commit complete.

SQL> select a,b from
2 (select a,b, (count(*) over(partition by b) / count(*) over() *100) as probabilty_to_hit_b from stats)
3 where b=probabilty_to_hit_b;

no rows selected

-- cool, although 0% is one of the possible answers, you're chance of getting it right is still 0%

ps: hmmm...isn't that a strange way to calculate percentages of data distribution? never mind, i'm a dba...

Thu Dec 01, 02:48:00 PM EST  

Anonymous Anonymous said....

Hi Tom,

Maybe we could consider it as two chain related questions.

question 1: Choose an answer to this question at random?
a) 25%
b) 50%
c) 60%
d) 25%

question 2: What is the chance you will be correct for question 1?

So 1/3 is the correct answer to question 2.

Fri Dec 09, 12:38:00 AM EST  

Blogger Thomas Kyte said....

@anonymous -

that assumes one of the answers is correct doesn't it...

Fri Dec 09, 12:46:00 AM EST  

Anonymous Anonymous said....

Forget about the question, forget about the answers in the options.

You have 4 options, out of which 2 are same. Assuming if one of the answer is right, 33.333... is correct.

Tom: when you said e. "None of the above", I guess it is not an answer to this question as the questions starts with "If you CHOOSE an answer". We always choose from what we have... What do you say?

Sat Dec 10, 01:37:00 AM EST  

Blogger Thomas Kyte said....

@anonymous

but is cannot be 33.3% since that is not one of the answers - so the answer is 0% but that cannot be the answer either

so, there is no answer, none of the above.

Sat Dec 10, 08:57:00 AM EST  

Anonymous Anonymous said....

Tom,

if you want to add e."None of the above", the questions becomes as below.

If you choose an answer to this question at random, what is the chance you will be correct?
a) 25%
b) 50%
c) 60%
d) 25%
e)None of the above

So, now we have 4 distinct options, which makes 25%(a or d) as correct answers :)

Well... since 33.333... is not in the options, you said it is not an answer. So, what if I add e.33.33 to the options, the answer still would be (a or d) :)))

Sat Dec 10, 08:32:00 PM EST  

Blogger Thomas Kyte said....

but that this the point - there is no answer to this question.

It is poorly phrased
It is ambiguous
It doesn't contain enough information to answer it


Like so many questions asked and not answered on forums and the like

Sun Dec 11, 08:48:00 AM EST  

Anonymous Anonymous said....

It is something like if you could go back into the past and change things so you would not exist in the future, would you immediately cease to exist in the past itself? Things which can really make your head hurt.

Sun Dec 11, 10:29:00 AM EST  

Blogger Balaji said....

Well I would choose "60%" as the right answer. Why? There is two way to answer multiple choice question. One by picking the correct answer or by eliminating wrong answers and I am going to follow the second. You have already proved 25% & 50% are NOT the right answers and left with 60% as the right answer

Tue Jan 17, 07:00:00 AM EST  

Blogger Thomas Kyte said....

@Balaji,

using your logic, it would be 33%, but not 60%. 60% would be a 3 in 5 option, it is not even in the cards for this one.

Tue Jan 17, 08:29:00 AM EST  

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