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Math Help - Help with multiplying large numbers by hand

  1. #1
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    Help with multiplying large numbers by hand

    Aight Guy's I don't really understand it, I could never do the math problems in order, I recently came from double figures on top and bottom, Now I doing triple digits on top and bottom, I am currently going to tutoring for math and other thing's my teacher is having me play a game called Latice however you say it.

    any tips would be great, I really wanna get into a 4 year school, I currently graduated high school last year, I just didn't get everything I needed to go to a 4 year school etc. so I am going to Huntington Learning Center for extra help they're helping alot I just wanna little extra for when I am not there.
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  2. #2
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    Quote Originally Posted by Stillen GLE View Post
    Aight Guy's I don't really understand it, I could never do the math problems in order, I recently came from double figures on top and bottom, Now I doing triple digits on top and bottom, I am currently going to tutoring for math and other thing's my teacher is having me play a game called Latice however you say it.

    any tips would be great, I really wanna get into a 4 year school, I currently graduated high school last year, I just didn't get everything I needed to go to a 4 year school etc. so I am going to Huntington Learning Center for extra help they're helping alot I just wanna little extra for when I am not there.
    Post a specific problem(s) and provide a detailed explanation as to where your trouble with the problem is and it will be much easier to help.
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  3. #3
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    Quote Originally Posted by TheMasterMind View Post
    Post a specific problem(s) and provide a detailed explanation as to where your trouble with the problem is and it will be much easier to help.

    when the number is a 3 digit number up top and bottom

    345
    678

    I can go do 5x8 4x8 and 3x8 with no problem but then when I have to start with 5x7 4x6 etc then I get lost.
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  4. #4
    Member TheMasterMind's Avatar
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    Quote Originally Posted by Stillen GLE View Post
    when the number is a 3 digit number up top and bottom

    345
    678

    I can go do 5x8 4x8 and 3x8 with no problem but then when I have to start with 5x7 4x6 etc then I get lost.
    This is hard to explain the long way but why don't you check this out Maths Online - Online solutions for Long Multiplication It provides a good explanation and takes you through step by step. (click the next-step button)
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  5. #5
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    Quote Originally Posted by TheMasterMind View Post
    This is hard to explain the long way but why don't you check this out Maths Online - Online solutions for Long Multiplication It provides a good explanation and takes you through step by step. (click the next-step button)
    thanks, I was just using those numbers as an example.
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  6. #6
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    Quote Originally Posted by Stillen GLE View Post
    when the number is a 3 digit number up top and bottom

    345
    678

    I can go do 5x8 4x8 and 3x8 with no problem but then when I have to start with 5x7 4x6 etc then I get lost.
    8*5= 40 so write down the 0 and carry 4.
    8*4= 32 so add the carried 4 to 32 to get 35, write down the 6 and carry the 3.
    8*3= 24 so add the carried 3 to 24, write down 27
    Your first row is 2760, the product of 8 with 345.
    At this point you should have
    _543
    _678
    2760

    Now, write a 0 under that first 0 to represent "moving over one place" and do the same thing with the second number, 7:
    7*5= 35 so write down the 5 and carry the 3.
    7*4= 28 so add the carried 3 to 28 to get 31, write down the 1 and carry the 3.
    7*3= 21 so add the carried 3 to 21 to get 24 and write down 24
    Your second row is 24150
    At this point you should have
    __543
    __678
    _2760
    24150

    Write down two 0s below the last "50" to represent shifting againeo the same thing with the third number, 6:
    6*5= 30 so write down the 0 and carry the 3.
    6*4= 24 so add the carried 3 to 24 to get 27 write down the 7 and carry the 2.
    6*3= 18 so add the carried 2 to the 18 to get 20 and write down 20
    The third row is 2070 but again shifted one place to the left.
    Now you have
    ___543
    __678
    __2760
    _24150
    203000
    Finally add those numbers.

    I put in those dashes to make everything line up correctly.
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  7. #7
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    The basic idea is that multiplying 345 by 678 all at once is too much to handle.

    So instead, we multiply 345 by (600 + 70 + 8).

    So we'll multiply 345 x 600, 345 x 70, and 345 x 8 separately.

    Then we'll add up those three products for our final answer.

    The notation shown above is a handy way to do all three multiplications in the same area. If you recall, when you multiply by a number that ends in some 00s, you can just pretend the 00s don't exist and then attach them to the right side of your product.

    345 x 70 is the same as 345 x 7 x 10.

    Anyhow, that's some explanation behind the algorithm. I'm proud of you for finishing up at high school and taking the time to go back and learn what you missed; better late than never!
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