I think you'll love this book especially if you have mental math anxiety or a fear of numbers but even if you don't I still think you'll like it it will teach you how to calculate almost anything in your head in seconds certainly faster than it would take you to put it into a calculator could you calculate either of these in under 10 seconds I guarantee by the end of the video you will be able to and in fact we'll have a little test where you can prove to yourself that that's the case so we'll do that at the end of the video so I want to share the book with you I'm going to show you what I like about it what you'll get from it after share some of the methods as well now I know what you're thinking you're either thinking this is all total nonsense and these methods won't work at all how dare you I wouldn't do that to you or you're thinking they might work for some people but they won't work for me because my brain just doesn't do numbers very well I'm going to prove to you that that's not true but first let's take a closer look at the book the book consists of 11 chapters the last chapter is chapter infinity and the first one is chapter zero which is a nice there's also two for wordss one by Bill Nye no not that one the other by the late James Randy and if you haven't heard of him you should look him up because he was a really interesting man and they set the tone of the book really well chapter zero will teach you some quick tricks like multiplying by 11 and squaring numbers that end in five but hold on a second because you probably already know how to multiply by 11 and square numbers that end in five but this is a different method one you probably don't know and it works incredibly well so why weren't we taught this in school I'm looking at you Mr Becket what's the square OT of 4761 it's 69 or what about 79838 by 4,547 well the answer is 3 b636 m381 386 okay what about this one what's 5 + 3 just checking you're paying attention so the book will teach you how to do 5x5 multiplication just about in your head if you're really serious about doing that and other things too like calculating the day of the week from the date it's a fun way of seeing what's possible what you can calculate in your head if you put some time and effort into it and have the right methods the chances are you probably won't make it to the five-digit multiplication in your head that's pretty hardcore and quite difficult even with these methods but however far you make it assuming you make it through the first chapter you will definitely improve your ability to do mental math and especially if you're a number phobe I think it could cure you of that so I think you'll really love it now I promised I'd Shar two of the methods with you they are coming up but before I do I just want to tell you that the author is actually a professor of maths so this isn't written by someone that doesn't know their stuff he's a professor of maths and also he's a mathematician he does live shows where he gets people up on stage gives them a calculator and challenges them to answer questions more quickly than he can his name's Arthur Benjamin and even if you don't buy the the book it's definitely worth watching his Ted Talk uh which I've linked to in the description so to multiply a two-digit number by 11 you just add the two digits together so in this example 5 + 4 is 9 and then you take the result of that the nine and you put it between the five and the four so 54 * 11 is 594 sometimes the digits will add up to more than 9 when that happens you just add one to the first digit so for example 68 * 11 well 6 + 8 is 14 so you take the four and you put it between the two digits but because it's more than 9 you add 1 to the six so that becomes 748 so what about squaring a two-digit number that ends in five well that's quite straightforward as well so you take the first digit of that two-digit number and you multiply it by the next higher digit so if it was 55 for example you would say five because that's the first digit of 55 multiply by the next digit up the next higher digit which is six so you say 5 * 6 but actually it's 50 * 60 so 5 * 6 is 30 but because we're saying 50 * 60 that's actually 3,000 and then you just add 25 which is 3,25 let's try another one let's try 65 well you take the first digit of 65 which is 6 you multiply it by the next higher digit which is 7 so you say 6 * 7 that's 42 but it's actually 60 * 70 so that's 4,200 and you add 25 and that's 4,225 it works with any two-digit number ending in five right it's your turn now now you know the methods 53 * 11 and 35 squar I'm going to flash the answer up on the screen really quickly and you can see whether you get it right the book's great because it is packed full of learning hacks which is what makes it so useful and if you like optimizing your learning then you'll love brilliant.org the sponsor of this video let me show you why brilliant is where you can learn math data analysis coding and AI 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