Woman Gets Driver's License After 950 Tries

mr crypto writes "From the BBC News article, 'A South Korean woman is celebrating after passing the written exam for a driving license — on her 950th attempt. After four years of trying, 68-year-old Cha Sa-soon finally managed to secure the 60 out of 100 points needed to pass the test.' Maybe some things should just not be."

Comments

Asian Drivers...

[kid_oliva]

What more needs to be said.

Re:Asian Drivers...

[spyder-implee]

Hahaha. Everyone's thinking it.

What are the odds

[Clipless]

With that many tries she should have been able to choose random answers and still pass the test with a 60% a long time ago

Re:What are the odds

[SpottedKuh]

With that many tries she should have been able to choose random answers and still pass the test with a 60% a long time ago

Nope, not if she chooses randomly for each question, each time she writes the test. Assume that for each of the 100 questions, there are four possible answers, only one of which is correct. So, you have a 25% chance of getting each question correct and a 75% chance of getting each question wrong, each time a random test-taker writes the exam.

The odds of passing a test are: the sum from c=60 to 100 of getting c questions correct.

The chances of getting c questions correct is (100 choose c) * (1/4)^c * (3/4)^(100-c).

Summing up from c=60 to 100, you are left with a probability of 0.1326834674 * 10^(-12) of passing the test, if you take it truly at random each time you write it. Basically, if you wrote the test truly at random, you would expect to have to take the test 7,536,733,998,027 times before passing. So, really, she did quite well ;)

Re:What are the odds

[dharana]

TFA says it was multiple choices so the odds are even lower.

Re:What are the odds

[jackspenn]

You're math is wrong, just so you know.

Re:What are the odds

[Dr. Evil]

This is the right math. My solver is a bit slow though:

attempts=0
while [ $score -lt 60 ]
do
score=0
i=0
while [ $i -lt 100 ]
do
q=$((RANDOM % 4))
a=$((RANDOM % 4))
if [ $q = $a ]
then
score=$(($score + 1))
fi

i=$(($i+1))
done;
attempts=$(($attempts + 1))
echo "$attempts: $score"
done
echo $attempts

Re:What are the odds

[MyLongNickName]

I used your method of calculating odds and found this lady had a 4.8 * 10^-13 change of getting zero or more right. It is amazing she didn't get a negative score...

Re:What are the odds

[MyLongNickName]

I reread the gp post, and noticed I left off the (100 choose c). I've never seen this nomenclature before, and assume it equates to what I've always seen" (n!)/(r! * (n-r)!). If so, I retract my above post :)

Re:What are the odds

[MyLongNickName]

His math is correct. Your grammar is wrong, just so you know.

Re:System is broken

[sa1lnr]

This is only the written part of the test, she still has to pass the actual driving part.

Eh

[ShooterNeo]

Is the woman illiterate? If you can read the questions on a multiple choice test with just 100 questions, you can memorize them. Heck, if you have a terrible memory, you could just memorize a few questions each attempt. Then look up all the answers. Or ask someone with a brain.

I'm suspecting the woman is simply not literate.

Re:Eh

[Fishmoney]

I'm guessing that Koreans use a different alphabet than we do. I'm guessing it's difficult for a 68-year-old to learn an entirely new alphabet. Just guessing...

Rich

[Fotograf]

she would have to be very rich here in Germany to make this stunt.

Re:System is broken

[oldspewey]

Who's taking bets on how long it will take before she kills someone?

This just in!

...and the test is multiple choice...

[popo]

...and (wait for it... wait for it...) there are only 50 questions.

Just wow. 950 attempts to PASS a 50 question multiple-choice test? Is it safe to assume she's illiterate?

Re:...and the test is multiple choice...

[Hognoxious]

Does it matter how many questions there are? The pass mark is usually expressed as a percentage.

Re:...and the test is multiple choice...

[FlyMysticalDJ]

in a small variation in the number of questions won't have a whole lot of difference when using a percentage to determine passing, but answering 8 questions right out of 10 is a LOT different from 800 out of 1000. Not to mention if she's illiterate, it would be slightly easier to slowly memorize what 50 questions and their answers look like than 100.

Re:...and the test is multiple choice...

[Hognoxious]

it would be slightly easier to slowly memorize what 50 questions and their answers look like than 100.

While they probably reuse questions, I doubt they use the same questions every time.

50 from a pool of 1000 would be a lot harder than 100 from a pool of 200. Though it's fair to say that with the number of times she's done it she's probably seen every question that could conceivably be asked anyway - several times over ...

Wait what?

[excalibur313]

I don't understand how someone can even take a test that many times since 2005. Thats like 2 tests every 3 days.