Breaking chocolate bar into small squares

You hear 3 snaps when someone breaks up a 2 × 2 2 \times 2 chocolate bar into 1 × 1 1 \times 1 pieces, 8 snaps when it's a 3 × 3 3 \times 3 bar, and 15 snaps when it's a 4 × 4 4 \times 4 bar.

How many snaps will you hear when an 8 × 8 8 \times 8 chocolate bar is split into 1 × 1 1 \times 1 pieces?

Details and Assumptions:

  • You cannot break two or more pieces at once.
  • Breaks must be made either horizontally or vertically.
31 47 55 63

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38 solutions

Jacopo Piccione
Sep 1, 2018

A simple solution is this. At the beginning we have only 1 piece and we have to end up with 64 pieces. Since we make only one extra piece with each cut, we have to cut the bar 63 \boxed{63} times.

Very intuitive solution.

Kelvin Hong - 2 years, 9 months ago

Sounds flawed without further explanation but it's still nice.

P P - 2 years, 9 months ago

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Not seeing how it's flawed.
Each crack increases the number of chunks from n chunks to (n+1) chunks. There is always at least one available move. There is no way to increase the number of chunks by more than one.

Richard Desper - 2 years, 9 months ago

Geometrically, you have 4 4x4 bars. You hear 60 snaps, which is 4 x 15. You need to hear 3 remaining snaps.

Jean Michel Henry - 2 years, 9 months ago

Its actually impossible. as the "condition" is that you cannot break two or more pieces at once, with a caveat that all breaks must be either horizontal or vertical, therefore as the definitions are "bar" and "pieces" (inferring a piece is a 1x1 square) you cannot JUST separate ONE piece. ;-)

Brett Jolly - 2 years, 9 months ago

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Sure, that's right. With his word piece he doesn't just mean a single piece he means any group of single-pieces, so you get a greater amount of groups of single pieces each time you break the bar, so there must be n-1 breaks to get n groups of single-piecea

Paul Kopold - 2 years, 9 months ago

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isn't a group of single pieces a "bar". He does actually use the word "bar". just fancied being pedantic today!

Brett Jolly - 2 years, 9 months ago

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@Brett Jolly I used the word "piece" for every group of single little pieces, and the word "bar" for the entire chocolate piece. Sorry for the misunderstandings.

Jacopo Piccione - 2 years, 9 months ago
Blan Morrison
Sep 9, 2018

You must snap the original grid seven times, and then snap each of the 8 rows/columns 7 times. This gives us 7 + 8 × 7 = 63 7+8\times 7 = \boxed{63}


If you notice the pattern, you might conjecture

If you have an n × n n\times n chocolate grid, then you will hear n 2 1 n^2-1 snaps to separate the bar into 1 × 1 1\times 1 squares.

Indeed, we can prove this. Using the same logic before, but only generalized: f ( n ) = ( n 1 ) + n × ( n 1 ) = n 2 n + n 1 = n 2 1 f(n)=(n-1)+n\times (n-1) = n^2-n+n-1=\boxed{n^2-1}

For the sake of completeness, the lower bound should also be established.

Joonas Jürgen Kisel - 2 years, 9 months ago

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I think it is quite obvious that the model is nonsense for n < 1 n<1 , so I figured that is not necessary.

Blan Morrison - 2 years, 9 months ago

Not needed in this case, as it is not establishing f(n+1) from f(n) :) Besides the lower bound n=2 is already established by the problem

Ni Ze - 2 years, 9 months ago

I used the same, but then how are we sure this is the minimum number of snaps ? :)

Ni Ze - 2 years, 9 months ago

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This is the most optimal way.

Blan Morrison - 2 years, 9 months ago
Chukwuka Odigbo
Sep 9, 2018

Trying to avoid complications, break the 8 by 8 bar into half, ie two 4 by 8 pieces. That's one snap.

Then, break the two 4 by 8 pieces each into half, that's four 4 by 4 pieces. Two more snaps occurred here.

2 + 1 gives 3 so far.

For each 4 by 4 piece, it's 15 snaps.

15 X 4 gives 60.

60+ 3 gives 63, and there you have it.

Paul Tan
Sep 9, 2018

2^n - 1 snaps where n is the n*n dimension of the chocolate bar

Wrong. 3x3 doesn’t work.

Petr Zenin - 2 years, 9 months ago

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He meant n^2 -1

Jaeden VAITHIANATHAN - 2 years, 9 months ago

It would be n^2-1, ;)

Pau Cantos - 2 years, 9 months ago

Can you prove this?

Blan Morrison - 2 years, 9 months ago

It's actually (n+1)*(n-1). 2^n - 1 grows way too fast.

Richard Desper - 2 years, 9 months ago
Sundeep Narang
Sep 9, 2018

Another easier solution is that a 8×8 bar will be four 4×4 bars, after 3 snaps, and each of those 4x4 bars will be 15 snaps. So total 3 + (15×4) =3 +60 = 63

This is especially easy since the problem states the solutions for a 4x4 bar and a 2x2 bar.

I.e. start by considering the 8x8 bar as a 2x2 bar where each of the pieces is actually 4x4 smaller pieces. Dividing up this 2x2 bar takes 3 steps (given in the description).

Now for each of the 4 thus obtained 4x4 bars, we know it takes 15 steps (again from the description). I.e. the total in this step is 4*15=60.

Add up 3 and 60, and we obtain 63.

Roland van Vliembergen - 2 years, 9 months ago
Hani Haddad
Sep 9, 2018

3, 8, 15... We can notice that we added 5 then 7 then it must be 9 etc. 3, 8, 15, 24, 35, 48, 63, 80... the 8th term is 63.

You cannot assume that the sequence will continue like that.

Blan Morrison - 2 years, 9 months ago

Nice try my freind

Jaafer Hosni - 2 years, 8 months ago
Chew-Seong Cheong
Sep 10, 2018

The general solution of the number of snaps for breaking n × n n\times n chocolate bar to 1 × 1 1\times 1 pieces is n s n a p s = n 2 1 n_{snaps} = n^2-1 . For n = 8 n=8 , n s n a p s = 8 2 1 = 63 n_{snaps} = 8^2-1 = \boxed{63} .

Lee-Ann Conlan
Sep 11, 2018

Snap the 8x8 in half and each half in half = 3 snaps

Now you have four 4x4 pieces

One 4x4 takes 15 snaps

Therefore 4 x 15 + 3 = 63

N Kansara
Sep 10, 2018

If there are n rows given then first we will break all rows by making n-1 snaps and then each column can be split by making n-1 snaps, thus for n rows we will make n (n-1) snaps. Therefore total snaps = n (n-1) + (n-1) = n^2 -1. In this case n =8 So number of snaps = 8^2 -1 = 63

Johanan Paul
Sep 10, 2018

You can break the 8x8 piece into four 4x4 pieces using 3 snaps. The value to break one 4x4 piece is given in the question (15 snaps). Hence, you need 4 15 + 3 = 63 4*15+3 = 63 snaps

if we split 8 × 8 into three chocolate bar as 7 × 7 and 1 × 8 and 1 × 7 individually,we hear 2 snaps then, recursion process to resolve problem which split 7 × 7 we hear the 7+8 = 15 times snap when we split into three chocolate bar as 7 × 7 and 1 × 8 and 1 × 7, include split 1 × 8 and 1 × 7 to 1 × 1 into chocolate bar 1 × 1 pieces.

def split(n): if n == 2: return 3 return split(n-1)+2*n-1 print(split(8)) 63

Each round of 3 snaps is capable of dividing a square chunk into even quarters. 3 for the first round plus 4 times 3 for the remaining 4 4x4 blocks, then iteratively again for each of the 16 remaining chunks gices 63. 3+(4 3)+((4^2) 3)=63

A simple Solution is to subtract 1 from the total of the the chocolate bar e.g 8*8=64-1=63 and it also works with other different shaped bars.

David Bronson
Sep 15, 2018

A strange solution I found is that if you add one to one side of the multiplywler and subtract one from the other side, it will always work. For instance if you have a 5x5, you adjust it to 4x6=24. I don't know why this works. Maybe soneone can explain?

Geneveve Tudence
Sep 14, 2018

Given the conditions, for NxN bar, the number of snaps could be shown through the formula (N-1) + N(N-1).

Note that for the NxN bars, the number of columns is N. With this, we can have (N-1) snaps done horizontally and it will give us N pieces of bars wherein each has 1xN dimension. To split all into 1x1 pieces, each bar of 1XN dimension will be cut into 1x1 pieces with N-1 snaps done vertically. Note that we have N bars of 1xN dimension. So, the number of snaps done vertically is Nx(N-1).

Note that the total number of snaps in NXN bar is the sum of snaps done horizontally and vertically.

Horizontally---- N-1 snaps

Vertically------- Nx(N-1) snaps

Thus, the total number of snaps in NxN bar is

(N-1)+N(N-1).

So, for 8x8 chocolate bar, we have

(N-1)+N(N-1)

=7+8(8-1)

=7+8(7)

=7+56

=63 snaps

Y n = (X o-X n) x (X o+X n) + Y o

For X o = 2, Y o = 3, and X_n = givenDimension

Jarod Rhine-Davis
Sep 13, 2018

I got the answer through (n-1) * (n+1).

When there are 64 squares, the answer is 7*9.

2x2 (=4) -> 3 snaps

3x3 (=9) -> 8 snaps

4x4 (=16) -> 15 snaps

... finding the pattern

n^2 - > n^2 - 1

... so, it can only be 63

8x8 (=64) -> 63 snaps

Mujahed Merae
Sep 13, 2018

(L×w)-1= # of snaps Ex (3×4)-1=11 snaps (4×5)-1= 19 snaps

Test it

Priyanshu Kumawat
Sep 13, 2018

Breaking a 2×2 chocolate gives us 3 snaps (2×2)-1 Breaking a 3×3 chocolate gives us 8 snaps (3×3)-1 Breaking a 4×4 chocolate gives us 15 snaps (4×4)-1 Therefore, breaking a 8×8 chocolate will give us (8×8)-1 = 63 snaps

Ginsederp Derpy
Sep 12, 2018

One way to break up a chocolate bar is to snap it in half, and snap its halves in half and so on.

This is binary recursive function with l o g 2 ( 8 8 ) = 6 log_{2}(8\cdot8) = 6 steps where each step contains twice as many snaps as the previous one 1 , 2 , 4 , . . . 1, 2, 4,...

Counting the number of snaps, you'll get the geometric progression 1 + 2 1 + 2 2 + . . . + 2 6 1 1 + 2^1 + 2^2 + ... + 2^{6-1}

Which will give you S 6 = 1 1 2 6 1 2 = 63 S_{6}= 1 \cdot \frac{1-2^6}{1-2} = 63

Robert Hedlerfog
Sep 12, 2018

We have 4 grids of 4x4 in a 64 square grid, we already know that for a 4x4 grid it takes 15 snaps so 4x15 for all 4 grids. Now we only need to add the number of snaps to divide the 64 grid into 4 separate grids which is 3. Therefore: 4x15+3=63 snaps for the total

Thomas Starucka
Sep 12, 2018

Each piece make one snap, except the final one

2x2 = 4➡️ 4-1 (1 is the final piece) = 3 snaps

3x3 = 9 ➡️ 9-1 = 8 snaps

4x4 = 16 ➡️ 16-1 = 15 snaps

...

8x8 = 64 ➡️ 64 pieces - the final piece = 63 snaps

when there is a 2x2 bar then there are 3 snaps ( 2^2)-1 when there is a 3x3 bar then there are 8 snaps ( 3^3)-1 when there is a 4x4 bar then there are 15 snaps **( 4^4)-1


thus,when there is a 8x8 bar then there are 63 snaps *( 8^8)-1 * thus the answers is 63

Saboor Khan
Sep 10, 2018
  1. Divide the one 8x8 piece into four 4x4 pieces.. This will take 3 snaps, 1 snap for halfing it into two 8x4 pieces and then 2 snaps for further splitting into four 4x4 pieces.. Now u r given that 15 snaps are required for reducing a 4x4 piece to 1x1. Since u have 4 pieces so 60 snaps plus 3 initial snaps gives u a total of 63 snaps.
Anmol Arichwal
Sep 10, 2018

If we divide it into four pieces then we get 4×4 type squares Now it is given that a 4×4 square needs 15 sounds So the answer is 15×4+3 Which is 63

Prem Chebrolu
Sep 10, 2018

n 2 1 n^{2} - 1 is the formula ( where n n is one side) to calculate the number of snaps!

So, here n = 8 n = 8 .

\therefore , number of snaps = = 8 2 1 8^{2} - 1 .

Which is 64 1 64 - 1 = = 63 \boxed{63}

Patience Patience
Sep 13, 2018

we can find thats n ^2 -1

Spriha Basir
Sep 12, 2018

In general...make square of 2,3,4...and then subtract 1....

Aaron Tang
Sep 11, 2018

Let f ( m ) f(m) donates the snaps you will hear when a m × m m \times m chocolate bar is split into 1 × 1 1 \times 1 pieces, then

f ( 2 n ) = 4 × f ( 2 n 1 ) + 3 f(2^n) = 4 \times f(2^{n-1}) +3

by the observation that we can split a 2 n × 2 n 2^n \times 2^n chocolate into 4 pieces of 2 n 1 × 2 n 1 2^{n-1}\times2^{n-1} chocolates by 3 snaps. thus

f ( 8 ) = 4 × f ( 4 ) + 3 = 4 × 15 + 3 = 63 f(8) = 4 \times f(4) + 3 = 4 \times 15 + 3 = 63

Jam M
Sep 11, 2018

It takes n 1 n-1 snaps to break an n × n n \times n square into n n 1 × n 1 \times n rectangles. Furthermore, n 1 n-1 snaps break each rectangle into n n 1 × 1 1 \times 1 squares. Hence, the number of snaps to break an n × n n \times n square into 1 × 1 1 \times 1 squares is n 1 + n ( n 1 ) = n 2 1 n-1 + n(n-1) = n^2 -1 . In particular, if n = 8 n = 8 , the number of snaps is 63 63 .

Josh Lagerwey
Sep 11, 2018

You need to snap it three times to break it into 4 pieces. Then you need to snap each of those three times to break each block into 4 new pieces. Now you have 16 piece, each of which need 3 more breaks. So, 3 + 3 4 + 3 16.

Ervyn Manuyag
Sep 11, 2018

64-1=63, cmon now

Ismael Savedra
Sep 11, 2018

Simple the bar is 8x8 pieces so 8x8-1

Yosef Scolnik
Sep 11, 2018

the second assumption - that you can break either horizontaliy or verticaly - make the problem imposible ! look at the 2x2 example - after the first cut - say vertical - you have to cut horizontally and vice versa !

Andrew Lopez
Sep 11, 2018

For every increase in n^2 you add the sequential prime number to the total number of snaps from previous answer. 2x2= 3 snaps...3x3= 3+5= 8 snaps.... 4x4= 8+7=15 snaps

Maybe you mean sequential odd number, because the 9 you add from 4x4 to 5x5 isn't prime...

C . - 2 years, 9 months ago

Of course that’s what I meant.. lmao! It was 3 in the morning!!

Andrew Lopez - 2 years, 9 months ago
Archit Wagle
Sep 10, 2018

Solve the recurrence equation T ( n ) = 4 T ( n 4 ) + 3 T (n) = 4T(\frac {n}{4})+3

What is T(1)? What is n?

Ossama Ismail - 2 years, 9 months ago

you mean 4*T(n/2)+3... And what if n is odd?

C . - 2 years, 9 months ago

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