View Full Version : Math brainteaser


Abi
06-19-15, 05:42 PM
You are on your way to visit your Grandma, who lives at the end of the valley. It's her birthday, and you want to give her the cakes you've made.

Between your house and her house, you have to cross 7 bridges, and as it goes in the land of make believe, there is a troll under every bridge! Each troll, quite rightly, insists that you pay a troll toll. Before you can cross their bridge, you have to give them half of the cakes you are carrying, but as they are kind trolls, they each give you back a single cake.

How many cakes do you have to leave home with to make sure that you arrive at Grandma's with exactly 2 cakes?

hint: this can be solved very quickly, in your head, without pen and paper.

midnightstar
06-19-15, 05:44 PM
14? 28? 973? :p

Abi
06-19-15, 05:45 PM
:lol:

dvdnvwls
06-19-15, 06:01 PM
Are there bonus points for estimating how much weight Troll #1 will gain, assuming we each have two grandmothers and none of us use Aspartame? :)

dvdnvwls
06-19-15, 06:04 PM
More to the point, do trolls require cakes to be cut in half when I'm carrying an odd number?

Abi
06-19-15, 06:04 PM
:lol:

Jokes aside, it's really easy.

hint: think about what you want to happen at the LAST bridge,and the answer should "hit" you.

Abi
06-19-15, 06:04 PM
presumably, but it doesn't matter.

Fuzzy12
06-19-15, 06:10 PM
You are on your way to visit your Grandma, who lives at the end of the valley. It's her birthday, and you want to give her the cakes you've made.

Between your house and her house, you have to cross 7 bridges, and as it goes in the land of make believe, there is a troll under every bridge! Each troll, quite rightly, insists that you pay a troll toll. Before you can cross their bridge, you have to give them half of the cakes you are carrying, but as they are kind trolls, they each give you back a single cake.

How many cakes do you have to leave home with to make sure that you arrive at Grandma's with exactly 2 cakes?

hint: this can be solved very quickly, in your head, without pen and paper.

2
6
14
30
62
126
244
490

Umm 490?

I doubt I got it right but if I did -> Very quickly without own and paper?? :mad: :mad: I didn't use pen and paper but it took me forever and made my brain hurt. :mad:

Love troll toll by the way :o

Actually I did sort of use pen and paper..by typing it out on here :scratch:

Fuzzy12
06-19-15, 06:14 PM
Hold on..is it 2????

2
1
2
1
2
...

:D

Cmon abi, don't make me sweat. 2???

Abi
06-19-15, 06:25 PM
Yay Fuzzy :) :) :)

Fuzzy12
06-19-15, 06:26 PM
Yay Fuzzy :) :) :)

I'm guessing it's 2 and not 490???

Abi
06-19-15, 06:29 PM
Yes fuzzy

Lunacie
06-19-15, 06:52 PM
You've got some 'splaining to do, Lucy.

How does it work?

Abi
06-19-15, 07:12 PM
You start with 2cakes
At each bridge, the troll takes half your cakes and gives you one back.
So if you start with 2, the trolls will always take half of 2 (1) and then give you one back, so you will always have 2 cakes, which is exactly how many you need.

BellaVita
06-19-15, 08:29 PM
Didn't you tell me this one over Skype before?

Lunacie
06-19-15, 08:29 PM
You start with 2cakes
At each bridge, the troll takes half your cakes and gives you one back.
So if you start with 2, the trolls will always take half of 2 (1) and then give you one back, so you will always have 2 cakes, which is exactly how many you need.

Ha! Dumb old trolls! :lol:

midnightstar
06-20-15, 05:45 PM
You start with 2cakes
At each bridge, the troll takes half your cakes and gives you one back.
So if you start with 2, the trolls will always take half of 2 (1) and then give you one back, so you will always have 2 cakes, which is exactly how many you need.

OK I'm officially the least logicest and mathicest member of ADDF :o

*puts it in my signature* :o

Little Missy
06-20-15, 08:03 PM
Are they really good cakes?

psychopathetic
06-20-15, 09:18 PM
Depends.

They're probably pretty good cakes.

I mean...you didn't make them did you?

/burn!!!

:lol:

Greyhound1
06-20-15, 11:22 PM
2 cakes would be all you would need