From The Derbyshire Email Bag: Math, Masks, And Rhinoviruses
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For some reason—a lot of people with time on their hands to read random bloggings, I guess—my March Diary brought in an unusually large quantity of email. Many thanks to all, and apologies for not being able to answer everyone individually.

The biggest subset concerned my Math Corner. I did indeed bugger up my algebra, at an embarrassingly elementary level.

I had proceeded by brute enumeration, just scribbling down all 35 best-of-seven possibilities, then counting— but of course mis-counting—wins in 4, 5, 6, and 7 games. The right way is to note that the number of ways of winning best-of-seven in n games is C(n-1,3), so correct coefficients in my formula are 1, 4, 10, and 20.

I haven't decided whether to blame my raging rhinoviruses for the blunder or to write it off as a Joe Biden moment.

One reader told me that this problem and several of the same kind are covered in Paul Nahin's 2000 book Duelling Idiots and Other Probability Puzzlers. Thank you, Sir, I'll check it out. only shows two available in hard copy, but there are lots at (Also available as an ebook for the young folk.)

Readers have also been free with diagnoses of my long URI, suggesting everything from whooping cough to you-know-what.

Three or four readers tell me that they, or someone close to them, have been similarly afflicted through the first weeks of 2020, fortifying my suspicion that something's going on besides, or below, COVID-19.

Richard Dawkins has tweeted that among the many, many viruses for what we loosely call "the common cold" are junior members of the coronavirus family.

Seems to me we have a lot to learn about this stuff.

A reader wants to know why, if I only wear a mask when shopping, the diary was decorated with a picture of me in my study, masked. That's easy: My editor emailed in when the March 20th Radio Derb was being posted asking if I could send across a picture of myself in a mask. I obediently put a mask on and clicked the vidcam.

Should my mask picture be interpreted as me taking sides in the raging masks-work / masks-don't-work debate? Nah. Wearing a mask is, for me, just chicken-soupery: it can't hurt

Also I messed up the Philippa link to my May 2017 diary: here you go. The Philippa there is Pippa Middleton, younger sister of Kate Middleton, Duchess of Cambridge. That Philippa may be the only person to have had a Facebook page dedicated to her rear end.

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