Do you have a good method for long multiplication which you could tell me. Eg 400 x 25 or 138 x 68?

Question

Do you know of a good method for long multiplication. I have a non calculator exam at the beginning of June so I really need to learn how to do it but I cant see to find a method that works for every question. Thanks

Answer 1

its easier to break it down into smaller sums:

400 x 25 = 4 x 100 x 25 = 4 x 25 x 100 = 100 x 100 = 10,000

138 x 68 = 70 x 138 - 2 x 138 = 7 x 138 x 10 - 2 x 138
= 966 x 10 - 276 = 9660 - 276 = 9384

Answer 2

write the long number above and the smallest down like that
138
68
then multiply the 1st no. above with the 1st no. below 8 times 8 = 64
write the 1st no. of the result which is 4 and keep the 6 in ur mind
then multiply the 2nd no. above with the 1st no. below then add the 6 (was in ur mind) to the result
3 times 8 =24 and + 6 = 30
write the 0 and keep the 3 in ur mind
then then multiply the 3rd no. above with the 1st no. below then add the 3 (was in ur mind) to the result
1 times 8= 8 and +3 =11
u write all of it as u finished all the number above
1104
then put 0 below the 1st no. of the result like this
1104
-----0
then multiply the 1st no. above(from the original problem) with the 2nd no. below and make the same steps but by multiplying each of the 3 numbers above with the 2nd no. below
8 times 6=48
3 times 6=18 and + 4=22
1 times 6=6 and +2=8
all the result is
1104
8280
then add these two no. to each other
9384

Answer 3

Find a good method that works for you and stick with it. Above all, practice alot before the exam. I use the method of the first example in the link that Ben gave you.

400
x25
-----
2000
800
-------
10000

Answer 4

What is wrong with the traditional method ?

138
X 68
..... 60 X8 ......6X8.+0. 480
60 X 30 .... 6x3 +00 1800
60 X 100 ...... 1X6 +000 6000







__________
add them up 8280

8X8...................................64
8X30 ......... 8x3 +0 240
8x100 8x1 +00 800
_________
add these up 1104

Add up the two sub answers

8280
1104
______
9384 total answer
=========
Any thing with zeros is easy
400 X 25 ===== 4 X 25 +00 === 10 00

Answer 5

divide the sum into smaller bits... ie 400x25 becomes 4x25 100 (plus the two zeros) so its ten thousand...

138x68 becomes 1x60 + 3x60 + 8x60 , and 8x1, 8x3 and finally 8x8... and you add your answers...

you can drop the zeros and add them back on, you can round up and subtract... and i often found it easier to do the sum backwards, working from the highest denominator, and adjusting the columns as you go...

long division is the same, chop it up into manageable sized sums, and add it up afterwards. always do a dirty sum, so you have a good idea where the decimal point goes ie 138x68 becomes 140x70 (14x7) 98 980 9800...

good luck and its dead easy once you get the hang of it..dirty math... works for me...

Answer 6

divide the given question into smaller bits and try answering them.......also u must have a reegular practice in order to cope up during examinations............all the best

Answer 7

Here's an example: http://en.wikipedia.org/wiki/Multiplication_algorithm#Long_multiplication

A search for "long multiplication" will yield more.

Answer 8

I suppose its a bit late to tell you to PAY ATTENTION IN CLASS!
Do that next time. :-)