a challenge for your able mathematicians

Chilli Queen · a challenge for your able mathematicians

I just got sent this by my dad. I thought it might be good for some kids in key stage 2 to challenge them to work out how it gets it right every time.

http://www.regiftable.com/regiftingrobinpopup.html

Moospan

How? How does it work? Please explain i never get these things!

Chilli Queen

There are actually only 9 possible answers. If you think of a 2-digit number and subtract the units digit you will always end up with the tens multiple. So
10-1=9
20-2=18
30-3=27
40-4=36
50-5=45
60-6=54
70-7=63
80-8=72
90-9=81

If you look at those answers in the table they always have the same 'prize', so whichever prize is randomly generated in those boxes will be the answer which appears in the thought bubble at the end.

Moospan

But how do they know what I am thinking of, I don't get it!! Am i moving my mouse over the box without realising?

Chilli Queen

They don't know what you're thinking. It doesn't matter which 2 digit number you start with you will always end up with the answer 9,18,27,36,45,54,63,72 or 81. All of those boxes have the same prize in which is randomly generated by the computer so it doesn't matter which one you're looking at. The final page is set to recognise which prize is in those boxes so it looks as though it is reading your mind.

queenie80

I have tried this about 10 times and like you moospan, just don;t get it! Even after your explanation, I just don;t get it!

I picked 18 twice and each time had different item and still got it!!!

Might use this with mine, just to let chn think I have some kind of magical power!!

Chilli Queen

Yes but the point is not what is in the box but the fact that you got the answer 18. You can't have the answer 17 or 19 or any other number which is not listed above. The computer randomly generates the same item to put in boxes 9, 18, 27, 36, 45, 54, 63, 72 and 81 e.g. a fuzzy scarf. Since you can't be looking at any other boxes and the computer knows it put fuzzy scarf in those boxes it will get it 'right'. Next time round it might put mouse mat in those boxes and as you will be looking at one of the boxes with mouse mat in it will get it right again.

bluerose

Took a while i now get it, i understand there can only be those possible answers the thing id not got was that each time you play they move the prizes around but those answers ie 9,18 etc all have the same answer what ever it is and thats the one that comes up and thats the one of course that we all got to as they are the only answers. simple when you get it but doubt id have got it without the explanation on here

Moospan

Ah!! i think i get it chilli!! Definitely can't explain to kids though!

Louiw

When you take away the 2 digits from your original number you are always left with a multiple of 9.
11 (11-1-1) =9
12 (12-2-1-) =9
13 (13-3-1-) =9 and so on t
until you get to 20
20 (20-2-0) = 18....
Look at the chart, all multiples of 9 have the same item, although it changes each time.....
Does that make sense?

dillsage

That is so coooool!