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PostPosted:Mon Feb 08, 2010 7:52 am
by wildrover
Yep - correct.

PostPosted:Wed Feb 17, 2010 11:27 am
by tonto
If 4928 is to 74,

and 3556 is to 58,

what is 2142 to?

PostPosted:Wed Feb 17, 2010 11:58 pm
by wildrover

PostPosted:Thu Feb 18, 2010 9:09 am
by tonto

PostPosted:Fri Feb 19, 2010 12:57 am
by pulse876
What is the next number in the following sequence:

2, 3, 7, 43, 13, 53

And if you are feeling very brave what is the number after that?

PostPosted:Thu Feb 25, 2010 10:39 am
by pulse876

PostPosted:Thu Feb 25, 2010 11:01 am
by wildrover

PostPosted:Fri Feb 26, 2010 12:57 am
by pulse876

PostPosted:Fri Mar 12, 2010 2:40 pm
by pulse876
This seems to have you stumped you all so the answer is:

Each term is the lowest prime factor of one more than the product of the previous terms.

[So 2*3*7*43+1 = 1807 = 13*139 (both primes) and hence 13 is the fifth term in the sequence.]

So the seventh term in the sequence is obtained by considering 2*3*7*43*13*53+1 = 1244335 = 5*248867 (both primes). Hence the seventh term is 5.

And the next term in the sequence is obtained by considering 2*3*7*43*13*53*5+1 = 6221671 which is prime and is hence the eighth term.

It is conjectured that if you keep repeating this process then eventually all the prime numbers would feature in the sequence (if you can have 'all' of an infinite number of primes). But of course the numbers involved in the multiplications would be rather large.

PostPosted:Fri Jun 18, 2010 4:28 pm
by wildrover
Topical one - in the World Cup each group contains four teams who play each other once with 3 points for a win and one for a draw. What's the maximum number of points a team can get and not qualify; and what's the minimum a team can get and still qualify for the next round. (Top2 qualify)

PostPosted:Sat Jun 19, 2010 12:23 am
by pulse876
The highest possible total number of points in the group is 18 (none of the six matches end in draws). So three teams could each end up with six points and one of them would be eliminated. So the most points you can get and fail to qualify is six.

If one team wins all three matches while the matches between the other three teams all end in draws then the group winner has nine points and each of the other three teams has two points. And one of those teams would qualify. But you can't qualify with one point so two is the minimum.

PostPosted:Sat Jun 19, 2010 9:45 am
by wildrover
Correct - and an extra mark for showing all your working out Pulse. :D

PostPosted:Fri Aug 20, 2010 10:51 am
by wildrover
You're down to the last 5 boxes on Deal or No Deal and you still have the £100K and £250K boxes. If you choose to go on, what are your chances of having either one or both of those boxes left when you get down to the last two boxes?

PostPosted:Fri Aug 20, 2010 1:56 pm
by JUS

1/5 +1/5 + (2!x(1/5x1/5)) ?????????

PostPosted:Fri Aug 20, 2010 6:52 pm
by wildrover
Nope - a good starting point is to work out how many different ways there are of picking 2 boxes from 5...