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Get well soon, Jess.

There are only 2 sets of number that can multiply to 36 and add up to an even number are
1, 4, 9 & 3, 3, 4
So SiFu have a 3 years old twin & a 4 years old.

Finally... there is an answer ! Thanks davidhome. Unfortunately its not it. The set 3,3,4 does not satisfy the 3rd condition "Đứa nhỏ nhất ..."

I'm not sure what you mean by "....add up to an even number". It is not required. What required is "Tổng số tuổi của tụi nó bằng số chai bia hai thằng mình uống hôm nay".

Therefore, there are several more sets if you care to look for, heheh
I'm sure someone will get it right !!!

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Get well soon, Jess.

In the question, as you said: "Đứa nhỏ NHẤT... " meant:
NHẤT = 1 => One of them is one year-old

"tổng số chai bia HAI thang uống" => trong quán nhậu, when 2 people drinking, they never let a person have less amount of drinks than the other, so that meant their amount of drinks are equal.
As begining... you said "sau VAI TUAN bia".... little bit awkward... I'm not sure it is part of the question or not. But after put together with the question...
VAI = X... I'll say X=2 cause it for 2 guys (1 for each)
TUAN=7
that's mean VAI TUẦN = 2 TUẦN => 14 = that's mean 14 chai bia

So.. tổng cộng số tuổi của ba đứa bé = 14
One of them is 1 year old
Only 1 group of number which have sume =14 and mult to 36 is 1 - 4 - 9

So từ nhỏ tới lớn 1, 4, và 9

^_^ hope it right

Very interesting analysis, shinichi . However, it is not quite right. For example,

- if your interpretation of the 2nd condition (2 tuần = 14) was correct, ie. the total beers consumed by the them is 14, then Sifu's friend wouldn't have to ask for the 3rd hint.

- the amount of beers taken by each person may or may not equal - not a must ! On my recent trip back to VN, I drank lots of beers with my old friends but I could never catch up with 'em .

- if the sum must be even, then there are other combos such as 1,1,36 and 1,3,12 may also be the correct answers too.

- "Đứa nhỏ NHẤT... " có nghĩa là đứa em út chứ không hẳn phải là 1.

There is one and only one set that requires all 3 conditions given. I'm sure someone will spot it.

Hope you guys didn't lose any hair on this yet ,
Lnd

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Get well soon, Jess.

Let me explain my answer
There are 8 combinations of 3 numbers that equal 36 are:
1, 6, and 6 (13)
1, 4, and 9 (14)
1, 3, and 12 (16)
1, 2, and 18 (21)
1, 1, and 36 (38)
2, 3, and 6 (11)
2, 2, and 9 (13)
3, 3, and 4 (10)
2 people drinking, usually is even amount of beer bottles, and that will give you:
1, 4, and 9 (14)
1, 3, and 12 (16)
1, 1, and 36 (38)
3, 3, and 4 (10)

Đứa nhỏ nhất trùng tên với...vợ mày.
This can not be 1 (Mợ mot?)

So the answer have to be 3, 3 & 4
they each drinking 5 bottles, total is 10
One of the 3 years old twin is a few minutes younger than the other.
The wife is Mợ Ba

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Get well soon, Jess.

I'm signing off - too busy shopping for wig.

Đứa con lớn 36 tuổi của bà lớn,bả đã đi bán muối nên SiFu về VN cưới vợ thứ hai,vì vợ trẻ đẹp nên chẳng bao lâu SiFu có thêm 2 đứa con,1 đứa được 1 tuổi mấy còn đứa kia thì mới chào đời.
Hai ông bạn uống 37 chai bia thì làm sao bạn của SiFu nhớ mình đã uống bao nhiêu chai nên hint thứ 2 vô dụng.
Hint thứ 3 :bạn của SiFu thường kêu vợ nó là...........................BABY .
Kết luận :tuổi 3 đứa con của SiFu là 36 ,1 ,BABY .