i spent the last 4 days rock-climbing, and managed to reach the summit of a rock structure several hundreds feet high [1];this, of course, is an excuse not to post any new thoughts on maths or the mathematician's life. so, if only to provide a somewhat mathematical flavour to this post ..

this week i am packing and sorting and playing host to my visiting family

"[This] must be done in your head only. Do NOT use paper and pencil or a calculator. Try to add up the following numbers as quickly as you can. Take 1000 and add 40 to it. Now add another 1000. Now add 30. Add another 1000. Now add 20. Now add another 1000. Now add 10. What is the total?"

~from Challenge Your Assumptions to Avoid Common, Frequent Mistakes @lifehacker

apparently the most common answer is 5000 (which is wrong).

[1]

*i would say that i climbed, with help, to the top of a mountain .. but strictly speaking, the rock structure couldn't possibly be high enough to be a mountain, much less a hill.*