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Some of his solutions are off the mark
on 17 April 2013
I am enjoying this book, if you like puzzles then its a bit of a laugh.
I'm disappointed though that some of his solutions are a little off the mark:
Q. Horse race: Given 25 horses, and you have a racecourse where you can race 5 horses at a time, how many races do you need to find the top 3 horses.
In his answer to this, the author shows it can be done in 7 races, but does not explicitly explain why it can't be done in 6, so doesn't quite answer the question.
Q. two men meeting after 20 years, one has 3 daughters whose ages have product 72 etc etc
In his solution, the author gives the prime factors of 72 as: 2, 3, 3 and 4???? 4 is not prime, so this is sloppy.
He then lists the possible combinations, but misses at least one combination - this could matter, but luckily he still gets to the right answer.
Q. If all families in a country plan their families as follows: "carry on til we get a boy, then stop", what will the male:female ratio be in the resulting population?
The author goes into long, complicated detail by splitting up into the various cases of family: B, GB, GGB, etc etc when this is not necessary at all: The answer is that, as long as no one aborts fetuses on the basis of sex, then the ratio will be just as it would if families did not have that strategy. He also makes a slightly incorrect assumption: Namely that the proportion of M:F is exactly 50:50. In reality, the ratio for live births tends to be very slightly more girls than boys (the ratio at conception is likely to be 50 50, but live birth ratios are very slightly different to that). 50 50 is pretty close.
Q. Desert island football, the only available coin for the toss is biased.
A better answer than the "google" and "microsoft" ones? Captain A hides the coin in one hand and asks captain B to guess left or right.