Saturday, May 16, 2015

'Cheryl's birthday' poser is back with Part 2: Cheryl's age

Source Website: http://news.asiaone.com/news/singapore/cheryls-birthday-poser-back-part-2-cheryls-age
By Lee Min Kok, mklee@sph.com.sg, The Straits Times, Saturday, 16 May 2015

Solution: https://vulcanpost.com/242212/solution-cheryl-birthday-part-2/
By Jolene Hee, Vulcanpost.com on 15 May 2015


Part 2: What's Cheryl's age?
PHOTO: Part 2: What's Cheryl's age?
PS: Dr Yeo has clarified that the second line in the puzzle should read: “Cheryl: I have two younger brothers.
Nanyang Technological University, Singapore with Un Cle Chai
By Lee Min Kok, mklee@sph.com.sg, The Straits Times, Saturday, 16 May 2015

http://3.bp.blogspot.com/-WXo6UzcQsV8/VVcq85BpJeI/AAAAAAAAgCA/7edWwpSI2CY/s1600/20150515_cheryls_age_ntufacebook.jpg
http://news.asiaone.com/sites/default/files/styles/full_left_image-630x411/public/original_images/May2015/20150515_cheryls_age_ntufacebook.jpg?itok=-_wqNbeu
http://news.asiaone.com/news/singapore/cheryls-birthday-poser-back-part-2-cheryls-age



SINGAPORE - First it was her birthday. This time, Cheryl's age is up in the air with a second part to the viral puzzle that made international headlines recently.

Nanyang Technological University (NTU) posted the question, which challenges people to work out Cheryl's age, on their Facebook page on Thursday night.

It also urged readers to grab a copy of its bi-monthly magazine, HEY!, to read more about Dr Joseph Yeo, the mathematics lecturer from the National Institute of Education who had set the now famous question as part of the Singapore and Asian Schools Math Olympiads (SASMO).

In an interview with The Straits Times last month, Dr Yeo shared that "Cheryl's birthday" was not a new logic problem and he had modified it by changing the names, date and context.

The question, which was leaked and made its way onto Facebook on April 12, generated a global buzz and was covered by media such as The New York Times, the BBC and the Guardian.

Question:
Albert and Bernard now want to know how old Cheryl is.

Cheryl: I have two younger brothers. The product of all our ages (i.e. my age and the ages of my two brothers) is 144, assuming that we use whole numbers for our ages. (Clue: 1)

Albert: We still don't know your age. What other hints can you give us?

Cheryl: The sum of all our ages is the bus number of this bus that we are on. (Clue: 2)

Bernard: Of course we know the bus number, but we still don't know your age. (Clue: 3)

Cheryl: Oh, I forgot to tell you that my brothers have the same age. (Clue: 4)

Albert and Bernard: Oh, now we know your age.

Solutions:

By Jolene Hee, Vulcanpost.com on 15 May 2015 and Bragadeesh

1) Cheryl: I have two younger brothers. The product of all our ages (i.e. my age and the ages of my two brothers) is 144, assuming that we use whole numbers for our ages. (Clue: 1)
(Clue: 1): Prime factorisation of 144 and list of possibilities

Prime factorisation of 144 and list of possibilities

Cheryl has two younger brothers and assuming order does not matter, there are lesser possibilities.

Cheryl has two younger brothers


2) Cheryl: The sum of all our ages is the bus number of this bus that we are on. (Clue: 2)
(Clue: 2): No use


3) Bernard: Of course we know the bus number, but we still don't know your age. (Clue: 3)
(Clue: 3): Sum of ages is not unique (i.e. it appear more than once). There left four possibilities.
3, 6, 8 and 4, 4, 9 add to 17
2, 8, 9 and 3, 4, 12 add to 19

Bernard: Of course we know the bus number, but we still don't know your age. (Clue: 3)


4) Cheryl: Oh, I forgot to tell you that my brothers have the same age. (Clue: 4)
(Clue: 4): 4, 4, 9

Cheryl: Oh, I forgot to tell you that my brothers have the same age. (Clue: 4)
So Cheryl is 9 years old
and her brothers 4 years old
The bus number is 17

By Lee Min Kok, mklee@sph.com.sg, The Straits Times, Saturday, 16 May 2015
This article was first published on May 15, 2015.
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