Problem: 277 * 524 Set it up like this: 5 2 4 2 7 7 Then multiply all the intersections (normally, you don't write this step). 5 2 4 2 5*2 2*2 4*2 7 5*7 2*7 7*7 7 5*7 2*7 4*7 to get 5 2 4 2 10 4 8 7 35 14 28 7 35 14 28 Now, we'll add up the numbers diagonally, starting at the bottom right. First diagonal: 28. Write down 8, keep the 2. Next diagonal: 2 + 28 + 14 = 44. Write down the 4 before the 8 so we get 48, keep the other 4. Next: 4 + 8 + 14 + 35 = 61. Write down the 1 to get 148, keep the 6. Next: 6 + 4 + 35 = 45. Write down the 5 to get 5148, keep the 4. Last: 4 + 10 = 14. Write it down to get 145148, which is the correct answer. If you have decimals, just do the same thing, then count the total number of decimal digits in both numbers (for example, in 1.23 * 4.56, it would be four) and set the point so that you get that number in the result (5.6088).
Well, "my" method, which is mathematically the same as the lines method, works nicely, even with very large numbers. Try to calculate 897979874 * 3948034 using the lines method...imaging you are in the desert and you want to calculate how much is 937 * 284 and you dont have your iphone with you...
Thats interesting, made me go to the wikipedia page: http://en.wikipedia.org/wiki/MultiplicationThe one used in Swedish schools mixes up the operations, so it's some multiplications, then additions, then back to multiplication, then addition and so on.
I wouldnt mind keeping myself preocupied playing in the sand with numbers, till hunger gets the better of me...Also, if I'm lost in the desert, math is low on my list of priorities...
I used the 'Long Multiplication' but you were using 'Lattice Multiplication'.Thats interesting, made me go to the wikipedia page: http://en.wikipedia.org/wiki/Multiplication
You were probably using th Egpytian method!? lol or maybe modern.
I dont actually know what method i use.
I wouldnt mind keeping myself preocupied playing in the sand with numbers, till hunger gets the better of me...
I was taught the long multiplication (or, rather, a slight variation of it), but that was 35 years ago and it's not the one they teach today. The current method, I'm sad to say, is one I haven't bothered to learn. (And don't get me started on division, I think they've changed method five times since I went to school, each time to the worse...).
I do a lot of math in my head. Usually, you only need an approximate answer, and I can usually find an approximate answer faster in my head than on a calculator. I almost never do arithmetics on paper, although I do use paper for algebra.I am from the old-school. Seldom used a calculator and, to say it all, I never "trusted" that much a calculator's answer..
I know the feeling. I've helped my step daughters and the the eldest girls boyfriend with high school and university (or, rather, the Swedish equivalents, as we cut the line between high school and university a little differently) maths, and it has been very rewarding. It's been fun seeing them grasp "math as a language" and get a feel for it. It's also been very developing for me. When I went to school som 25 years ago, I just learned "how" and pretty much skipped the "why", because that's all that was needed to ace the tests. However, as I helped them, I realized that, from the experience gained by using the math over the years, I've also gained an intuitive understanding of the "whys".Today I am an ex-teen ager (more or less) and my math abilities faded somewhat, but you won't believe how much I enjoy helping my son with his homeworks..a good excuse to listen to some AC/DC tracks while letting my writing hand fly on paper!