Three people go to seven eleven and buy three drinks. The cost is 30 dollars so each brings out a 10 dollar bill and pays the cashier.

When the three people are leaving, the cashier realizes that the three drinks only cost 25 dollar so he sends his assistant to give them 5 dollars back. The assistant thinks it will be difficult for them to divide the 5 dollars so pockets 2 dollars and gives them 3 dollars back.

Initially they paid 10 dollars each for the drinks. After they got back 3 dollars, their cost was 9 dollars a drink. So 9 times 3 is 27 and the assistant put 2 dollars in his pocket. 27 plus 2 is 29. Where did the dollar go?

RatoBhaleyji,

Cashier keeps $25

Assistant keeps $2

Buyers get $3

25+2+3 = 30

It works.

Learn Venn Diagram: this is a union problem where events are not mutually exclusive, i.e. you have to subtract the stuff ([n-1] times) that is counted multiple (n times) times. I mean count events only once: no duplications.

P(A OR B) = P(A) + P(B) - P (A AND B)

 

Good Luck, RatoBahley.

 Certainly looks like a Venn diagram material, however mutual-exclusion formula stated by GP  is  used to avoid over counting. Here we have under counting.
Heres what I think (without formulas):

There are 3 kinds of costs involved here.

a) Actual cost = 25/3 =$8.333333333......per Person
b)Overcharged cost = 30/3  = 10 dollars per person.
c)Charge Assumed by the question = (30-3)/3=9 dollars per person.

Hence  equating a) & b):
 they over paid 10-8.3333... =$0.6666... cents per person

c) total money overpaid by them = 0.6666..*3 = $2.00

This extra money is what the Assistant kept for himself.

conclusion: There is a bug in the question in this line:
"After they got back 3 dollars, their cost was 9 dollars a drink"

As we can see, their cost was not $9, Their cost should have been $8.3333 per person.

Eyefusion,

I am talking about issue on $29 where you count $2 taken assitant twice. Please read the original question, again.

There is double counting $25+2+2=29. That is where the writer was trying to confuse us.

 "After they got back 3 dollars, their cost was 9 dollars a drink." is a false statement.

Yesto ni jhuto bolna paainchha sajha maa aaesi?

 

 

 

the last line is false,  they paid 27$ in aggregate (after they got their refund of 3$) . Assistant put 2$ out of 27 $ so 27$ minus 2$ is 25$ which is actual cost of the drink (that cashiers took). It should be 27 minus 2 to get 25 not 27 plus 2 to get 29.

(point should be noted that, they paid only 27$ because they already got their 3$ back so we can't go towards 30$ mathematics instead it should be 27$ mathematics)

This math must be done when drunk.

GP ji, I read the question by OP and, I read your response. You just wrote down the generic mutual exclusion principle formula. You did not mention anything "about the issue of $29".

You arrogantly announce  "Learn Venn Diagram" in the first sentence of your response, and then  you don't follow up your answer clearly. And now, you ask me, politely though, to re-read the question again.I read the question. I understand the question. Chill a little buda ba.
Actually, I was a little ticked off by your "learn Venn diagram" comment. Otherwise I wouldn't have included your name.

Eyefusion:

Actually your conclusion is wrong on the following.

"After they got back 3 dollars, their cost was 9 dollars a drink"
"As we can see, their cost was not $9, Their cost should have been $8.3333 per person."

I understand Ratobhale wanted to confuse us. By saying "cost is $27 plus 2 = 29 where does $1 go?" But the thing is cost is $27 [25 (taken by seven eleven)+ 2 (assistant)] right. He should have added $3 that they got back from assistant, NOT $2 which is a part of cost.

Krishna and GP are getting the gist of it. They are correct.

Rascaal is also not right. The cost is $27 and dividing it by 3 = $9. He is right.

Yeah guys take it easy. This is a confusingly interesting question that's why I shared it with you. In fact it is a really stupid question. What if the cashier had given back say 8 dollars and the assistant put in two dollars in his pocket and gave each person two dollars back? Then since they got back 2 dollars it would have cost them 8 dollars per drink. 8 x 3 = 24. The assistant took 2 dollars. So the total is only 26 dollars where did the 4 dollars go? Yes I admit it was a stupid question but it reminds us the beauty and importance of paradigm shift. The whole paradigm was shifted from the cashier to the assistant and the customers when the cashier gave the cash to the assistant. Reality was that the cashier always had the 'missing' amount

Raascal you are wrong. I never lied when I said their drink cost 9 dollars each after they got a dollar back each. For them it did. Think about it. They paid 10 dollars initially and they got back a dollar each. So they paid 9 dollars each for their drink.

They paid 9 dollars each so total cash that's out = $27
The cashier had = $25
The assistant had = $2
Makes sense = yes!

So Raascal = wrong!

Eyefusion, your logic is correct but the cost to the customer was $9 each, however the PRICE (that was charged by shop) was $8.3333 each

Eyefusion,

Humor khoi kaha gayo! Yo thread ko gist ho humor! fun! By adding Venn Diagram, I wanted to add one more confusion.

P(A) = 27 (actual amount paid by these 3 people)

P(B) = 2 (second part of the main question: account keeps this money)

P(AB) = 2 (the money kept by accountant is already a part of P(A)

P (A OR B: amount paid / kept) = 27 + 2- 2 = 27.

The original question had $29 after distributing $1 to each of the 3 guys. So, question was on that excess $2 if you look from $27, and missing $1 if you look from $30 (assuming that you forgot returned amount).

It is again like a motorbike riding ant hits a tree, then a listener is asked what happened to the ant?  Listeners got puzzled, and asks a question back to story teller, because the story teller has already puzzled you with silly / funny answers, so the listener does not want to be fool again.

The answer is: Ant had a helmet..... Don't try to be rational in an irrational question.

I know one of my "friend" here used to tell such funny jokes on ant including this mathmatical question. These Qs are designed to have fun, but Timi ta malai gali galouse po garna kasiyou ta. Thulai shor ma.

Kasto rish uthya hola ta: Yastari sarpna thaleko: Lou hera ta.... "You arrogantly announce  "Learn Venn Diagram" in the first sentence of your response, and then  you don't follow up your answer clearly. ....."

Jai hos timro. Timro kalyan hosh. Santi milos, sukh milos, ani yo winter vacation / semester break (if you have) ramro sanga bitos. Feri malai gali nagar la,  babu raja.

GP

How can you say, beer costed 27 dollors? If it costed 27 dollos, why did the shopkeeper charge 25 dollors only???

Problem:  (Shopkeeper's price = 25)   !=  (Three guy's beer's value = 27 :: as thought by Ratobhale which is wrong)

Money is not lost anywhere.

Initial Scenario:

$10 x 3 buyers = $30  TOTAL

Final Scenario:

($ 1 per buyer) x 3 buyers  +  $2 (Assistant) + $25 (at Shop OR with three person as 'beer') = $30 TOTAL

Total Money at : Initial Scenario = Final Scenario

DONT THINK IN COMPLEX WAY!

Problem in Intial Question: "After they got back 3 dollars, their cost was 9 dollars a drink. So 9 times 3 is 27 ..."  IS WRONG.! Actually, 27 is NOT 'total cost' but it is 'total cost + asssistant's 2 dollors'. Total cost of beer is therefore 27 - 2 = 25 (NOT 27) which means 25/3 = 8.6666 dollors per head.  [if 27 were the total cost as cited, then "27 (now beer value) + 2(Money) + 3(Money)" = 32, ... from where came 2 dollors now??- would be the scenario, which is wrong...].. But we can not say 27 (beer value)..

SO, (8.6666 x 3 + 2) is what the three guys paid after they got 3 dollors refund. Therefore, 8.666x 3 + 2 + 3 = 30.

Brian Malfunction

I was pointing out the difference between cost and price

Cost is what something costs to you. In this case each drink ended up costing 9 dollars each because each person paid 9 dollars for it. This is a fact. This is the cost for the customer. You cannot deny this!

8.666 is the price that was charged by the cashier. the remaining two dollars were taken by the assistant.

It's time to move on from this funny confusing tale which continues to confuse many till this day.

America ma career develop garna bhanera Nepal dekhi Bau le bhrastachar gareko sampati le padhna aayeka haru ko Buddhi herda malai daya lagchha. Yasta Buddhi bhayeka janta bhayeko desh ko kaha bata development hunchha??