Discussion about math, puzzles, games and fun. Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ π -¹ ² ³ °

You are not logged in.

- Topics: Active | Unanswered

**khushro****Member**- Registered: 2015-04-10
- Posts: 2

The solution was very disappointing. It was just a straight-forward counting of the number of objects, which even an idiot with a calculator can do. There was nothing puzzling about it.

I was expecting a more mathematical solution, which would give the correct answer for n days instead of 12, and then substitute n=12 in the answer. Would not remain a starter, but would at least be a puzzle.

Offline

**phrontister****Real Member**- From: The Land of Tomorrow
- Registered: 2009-07-12
- Posts: 4,609

Hi khushro,

Yes, the given solution method is rather starter-ish.

A more satisfying solution exists, however, which by way of a nice mathematical formula in terms of *n* eliminates all that counting and will instantly display the answer for *n* (eg, *n*=12) days.

The formula can be found on the net, but, if you'd like to have a go at constructing it yourself, then here are a couple of hints (should you need them):

*Last edited by phrontister (2015-05-20 13:58:17)*

"The good news about computers is that they do what you tell them to do. The bad news is that they do what you tell them to do." - Ted Nelson

Offline

**Laatokka****Member**- Registered: 2016-06-07
- Posts: 1

Hi,

And if you want, you can try making a little program and modify it

(JavaScript)

var x = 1;

var y = 2;

var days = 1;

var PresentsPerDay = 0;

while (days < 13){

PresentsPerDay=x+PresentsPerDay;

x=x+y;

y++;

days++;

Offline

**phrontister****Real Member**- From: The Land of Tomorrow
- Registered: 2009-07-12
- Posts: 4,609

True!

A similar program in BASIC:

```
x=1
y=2
d=1
ppd=0
WHILE d<13
ppd=ppd+x
x=x+y
y=y+1
d=d+1
WEND
PRINT ppd
```

And...welcome to the forum!

*Last edited by phrontister (2016-06-07 23:10:17)*

"The good news about computers is that they do what you tell them to do. The bad news is that they do what you tell them to do." - Ted Nelson

Offline

**chinnu03****Member**- Registered: 2018-08-08
- Posts: 1

I have found the general solution for this puzzle,

For number of days = n

Total Presents = n(n+1)(n+2)/6

This can be derived as follows

Presents for n'th day = n(n+1)/2 because it is the sum of numbers from 1 to n.

Total presents till n'th day = Σ n(n+1)/2

Simplifying we will get the above formula

Hope it is helpful.

Offline

**bob bundy****Administrator**- Registered: 2010-06-20
- Posts: 8,453

hi chinnu03

Welcome to the forum.

Good result. But I'm afraid it has been done before. This was, for a while, a GCSE maths project in the UK. You'd get a grade 'C' for what you have posted but would need to show the whole proof and try possible extensions to get an 'A'.

Bob

Children are not defined by school ...........The Fonz

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

Sometimes I deliberately make mistakes, just to test you! …………….Bob Bundy

Offline