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Archive for October, 2013

## Circle of Friends

Posted by Chris under MathsChallenge (26 Responds)

Some friends sat in a circle. Each had a whole number of dollars. The first had \$1 more than the second, who had \$1 more than the third, and so on. The first gave \$1 to the second, who gave \$2 to the third, and so on, each giving \$1 more than s/he received, as [...]

## Ball bag

Posted by Chris under Logic (11 Responds)

A bag contains either a white ball or a black ball, and each case is equally likely. A white ball is added. You now randomly take a ball from the bag. If it is white, what is the probability that the remaining ball is white?
I’m not sure if this has been posted before.

## 9999

Posted by Chris under MathsChallenge (7 Responds)

What are the last N digits of 9^(9^(9^9))? That’s a power tower of nines.
Make N as large as you can. Personally, I’m not going to aim beyond N = 8 as far too much work would be involved.
I’ve discussed the maths you need in my last post. You will need to use a 9+ [...]

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