On the last day of xmas..

[BrowneIssue]

This is one of my favourite puzzles...

My true love came to me and said she's a bit hard up this year from being on the bench. Instead of giving me gifts over 12 days, she would give one gift per day. Thus:

Day 1 (Boxing Day) a partridge in a pear tree.

as per usual. Then:

Day 2 a turtle dove
Day 3 the other turtle dove
Day 4 another partridge in a pear tree

which I would have had on the 2nd day. This is followed by:

Day 5 The first of three French Hens

and so on.

Since she intends to start doing this on December 26th this year, on what date will I receive the final gift?

First to answer gets some bananananas and a sack of kudos.

[meridian]

January 2nd.

First to answer gets some bananananas and a sack of kudos.

Am I the first to answer?

[BrowneIssue]

Am I the first to answer?

Yes, you are. Enjoy both your bananananas.










Smartarse.

[meridian]

Why thank you.

Would the answer be Christmas Day?

(Actually, Christmas Eve because it's Leap Year next year...)

[BrowneIssue]

Why thank you.

Would the answer be Christmas Day?

(Actually, Christmas Eve because it's Leap Year next year...)

And you didn't even fall for the Leap Year Gotcha!

Well done!

...

Your tree's gone...

[MrRobin]

January 2nd.

Ay?? I make it 12th March

[BrowneIssue]

Ay?? I make it 12th March

12/03/2008? How do you get that result (which is wrong, as was 2nd Jan 2008).

[BrowneIssue]

Ay?? I make it 12th March

12/03/2008? How do you get that result (which is wrong, as was 2nd Jan 2008).

Oh, I see.

a) you forgot days 1 to 11. A day in March 2008 would only be enough days for the gifts originally intended for 12th Day.

b) Did you start on Xmas Day, rather than Boxing Day?

[MrRobin]

Ahhh. I see now. Sorry I read the question wrong. I didn't realise when you go to a new gift you have to also go back through all the previous gifts too before going onto the next one (just like in the song, Robin.. duh!)

OK so it's

12 ......n
SUM [ SUM(m) ]
n=1 ....m=1

which is 364 days from Xmas day, since the first day of presents is on Boxing day which is December 23rd (as next year has Feb 29th)

[BrowneIssue]

Ahhh. I see now. Sorry I read the question wrong. I didn't realise when you go to a new gift you have to also go back through all the previous gifts too before going onto the next one (just like in the song, Robin.. duh!)

OK so it's

12 ......n
SUM [ SUM(m) ]
n=1 ....m=1

which is 364 days from Xmas day, since the first day of presents is on Boxing day which is December 23rd (as next year has Feb 29th)

You are quite right.

And I made an absolutely classic error: one of the programmer's fencepost errors.

I took 26/12/2007 + 364 presents = last present on 24/12/2008. Which is wrong because present one was given on 26/12/2007, not 27/12/2008.

--------------------------------------------------
Explanation of fencepost errors follows:

1. Between my house and the neighbour's house I want to erect a fence of 1 metre fence panels. The houses are 10 metres apart. How many fenceposts are needed? Nine: because the end two fence panels are secured at the outermost ends against the houses.

2. At the bottom of the garden I want to erect a fence of 1 metre fence panels. The garden is 10 metres wide. How many fence posts are needed? Eleven: because each fence panel needs one at the start but the final panel needs a post at the end as well.

I started counting the days from 27/12/2007 and should have started form 26/12/2007. So on day zero I receive present one therefore on day 363 I receive present 264. Duh!
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Mr Robin, you are indeed the brave red-breasted hero at the top of the Christmas banananana Tree. And I am a plank.

Well done!


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