Customer Reviews

Brain Teasers

5 star:		(11)
4 star:		(1)
3 star:		(0)
2 star:		(2)
1 star:		(3)

 

 

Wow! This book is so much fun. But I am warning you that it is also very addictive so make sure that you have the time and patience. I would love to see some follow-ups since I'm almost all the way through. Thanks!!!

The answer to Brain Teaser #18 is incorrect. !Spoiler Alert!







The answer should be 27000001.

The problem is that all the digital sums are not 55 as the answer key suggests. For example consider the pair:

(10 - 999,990)

Here the digital sum is 46!

In fact if you break it down only 450000 of the sums are 55, 45000 of the sums are 46, 4500 are 37, 450 are 28, 45 are 19 and 4 are 10.

So the method of solution is not viable because the above would be difficult to figure out (I used a computer).

Rather the proper analysis is to show that each place value contributes 100000 of each number for 1-999,999 (e.g, there are 100000 1's in the ones column, 100000 1's in the tens column, and so on)

So you get

600000 * 1 + 600000 *2 ... 600000 *9 =
600000 (1+2+3+4+5+6+7+8+9) =
600000 * 45 = 27,000,000

But you need to add 1 for 1,000,000

So the final answer is 27000001

This is also verified by the following Mathematica brute force program:

digitalSum[x_] := Total[Flatten[IntegerDigits[Table[i,{i,1,x}]]]]
digitalSum[1000000]
27000001

Don't know of any other mistakes and otherwise the book is excellent!!

The problem with many "brain teaser" books is that they all have many of the same questions. That is not the case with this book. The questions in this book are challenging and fun. Makes for a great book to keep at the office to break up the monotony of the work day.

I have no one to blame but myself. I use riddles in my class to get my students to use their thought process in a logical manner. This book is more math text than riddle. Brain teaser? Math homework...

I was excited to get this book as a gift but found that most of the puzzles have already been seen in other books that I used. There were a few new ones but probably not enough to justify buying it.

This is a great book for brain exercises. I bought it for my husband, but our college-age children actually enjoyed it more! They challenged each other to solve the puzzles and made a little competition out of going through the entire book.

This puzzle book is on the mediocre side - there are very few puzzles overall, and no original content. It's just some puzzles the author has collected over time.

I bought this book as I was preparing for job interviews. Within 5 minutes of this book's delivery, I realised that this was complete junk. Its a small book with very few problems and there are really big blank places between two consecutive questions. Most of the problems are completely useless if you are preparing for quantitative interviews and the ones which are there are mostly fairly well known in puzzle circles. If you want a comprehensive good book stick to Xinfeng Zhou's guide book which has some of the really good (and hard) math puzzles that are commong among interviewers. John Kador's book is also decent.

This is a very well written book geared towards youngsters interested in probability, logic and solving puzzles. The author is one sharp chap - with degrees from Stanford and Harvard on his resume! This is also an excellent resource for poker and chess players - helps sharpen the mind. The book could have used more illustrations and the narrative could be more lively. But overall, a really good book that engages the brain. Would be an excellent gift for a high school student.

My husband loves challenging puzzles, and he really enjoyed this book. I just wish the author had written more books - I'm having trouble finding another quite like it.