Math Antics - Multi-Digit Multiplication Pt 1 - Free Educational videos for Students in K-12 | Lumos Learning

Math Antics - Multi-Digit Multiplication Pt 1 - Free Educational videos for Students in k-12


Math Antics - Multi-Digit Multiplication Pt 1 - By mathantics



Transcript
00:03 Uh huh . Hi and welcome to Math Antics .
00:08 In this video lesson , we're going to learn how
00:10 to do basic multi digit multiplication . Now this can
00:13 be tricky at first but don't get discouraged . It
00:16 just might take some extra time and practice but you'll
00:19 get the hang of it . One thing I want
00:21 to mention before we start is that multi digit multiplication
00:24 will be much easier for you . If you memorize
00:26 your basic multiplication facts , but if you don't have
00:29 them memorized , then be sure to have a multiplication
00:32 table handy when you're doing your practice problems . Okay
00:36 . The best way to learn this is to jump
00:37 right in . Let's try 137 times five . Now
00:42 as you can see this is a three digit number
00:44 times of one digit number . When you're given a
00:47 problem like this where the numbers are written side by
00:49 side , you need to rewrite it and stacked form
00:52 with the ones places lined up the way we did
00:55 with addition and subtraction . Now you might remember with
00:58 multiplication that the order of the problem doesn't matter .
01:01 So we can put whatever number we want on the
01:03 top or the bottom , but it's always best to
01:06 put the number with the most digits on the top
01:09 and the one with the fewest digits on the bottom
01:11 there . Now we draw our answer line below and
01:14 we put our time symbol to the left . So
01:16 we don't forget that we're multiplying . Okay , now
01:20 we're ready to learn the procedure for multiplying basically what
01:23 we're gonna do is break up this big multiplication problem
01:26 into a series of small multiplication problems or steps .
01:30 Those small steps involved multiplying two digit in the bottom
01:33 number by a digit in the top number . Now
01:36 in our problem we only have one digit on the
01:38 bottom and we're going to multiply it by each of
01:41 the digits in the top number . And since the
01:43 top number has three digits , that means that our
01:46 problem will have three small multiplication steps . For the
01:50 first step we multiply the bottom digit five by the
01:53 digit in the ones place of the top number which
01:55 is seven . We always start with the ones place
01:58 and work our way from right to left . So
02:00 five times seven gives us 35 . Now , just
02:04 like with addition when we get a two digit answer
02:06 , we have to carry the first digit to the
02:08 top of the next column because it will be in
02:10 the way of the next answer digit if we don't
02:13 . So the five stays down here in the ones
02:15 place of the answer . But the three gets carried
02:17 up to the top of the tens . Place calm
02:20 . Now it's time for the second step we multiply
02:22 the bottom digit five by the next digit to the
02:25 left . And our top number three . So five
02:28 times three equals 15 . But wait a second .
02:32 There's that three we carried up to the top from
02:34 the last answer . What do we do with that
02:36 ? Well we need to add it to the answer
02:38 that we just got . That's because that three was
02:41 supposed to go in the tens place of the answer
02:43 but just not all by itself . We had to
02:45 do the second multiplication step first and see what else
02:49 needed to go in that answer spot with it .
02:51 And it turned out to be a five , the
02:53 second digit of the answer 15 . So we have
02:55 to combine the two digits that both go in that
02:58 answer place . That's why we add the digit we
03:00 carried and we end up with 18 . But once
03:04 again our answer is a two digit number . So
03:06 we leave the eight in our answer line and we
03:09 carry the one up to the top of the hundreds
03:11 place column . Now for our third and last multiplication
03:14 step we have five times one which is just five
03:18 . But again there's that digit we carried up above
03:20 so it wouldn't be in the way . What do
03:22 you think we do with that digit , yep ,
03:24 we added to the answer we got from the multiplication
03:27 step , so five plus one gives a six and
03:30 that's what goes in our answer line . Okay then
03:33 we've done all three of our multiplication steps and the
03:36 answer to our problem five times 137 is 685 .
03:41 Now that wasn't so bad , was it ? Let's
03:44 try one more example before you practice some on your
03:46 own . Let's multiply 2617 by four . Again we
03:52 stack our problem with the ones places lined up and
03:55 we make sure that the number with the most digits
03:57 is on top . Because our top number has four
04:00 digits this time it means we'll break this problem up
04:03 into four small multiplication steps will multiply the bottom digit
04:07 by each digit in the top number , starting with
04:10 the ones place on the right and working our way
04:12 left . Okay here we go with the first step
04:15 we multiply the bottom digit by the top digit in
04:18 the ones place four times seven equals 28 . Because
04:22 we have a two digit answer , we need to
04:23 carry the digit that will be in the way we're
04:25 going to add it back in after we complete the
04:27 next multiplication step . So we carry the to to
04:30 the top of the 10s column and we leave the
04:32 eight where it is Now we can do the second
04:35 step . We multiply the bottom digit by the next
04:37 digit in the top number four times one equals four
04:41 . That was easy . But don't forget about that
04:43 digit we carried . We need to add that to
04:45 our answer from the second step . So four plus
04:48 two gives us six and that's what we put in
04:51 our answer place and this time we have one digit
04:54 answer so we don't need to carry . We can
04:56 just move on to the next step For our third
04:59 multiplication step will multiply four times six and that gives
05:02 us 24 , yep , it's a two digit answer
05:05 . So we'll need to carry again . The four
05:07 stays in the answer and the two moves up to
05:10 the top of the thousands , calm Now it's time
05:13 for the 4th and last step we multiply four times
05:16 two which is eight but then we need to add
05:19 the digit we carried , which is a two .
05:21 So eight plus two gives us 10 . And that
05:24 can go down in our answer line even though it's
05:26 a two digit number we don't have to carry because
05:29 we're all done with our multiplication steps and we have
05:31 our final answer four times 2617 equals 10468 . All
05:40 right . That's the basics of multi digit multiplication .
05:43 But it's really important to practice so you get good
05:45 at it . Be sure to do the printable exercises
05:47 for this section . Then once you think you have
05:50 it down , you'll be ready to move on to
05:52 the next video and learn how to do multiplication .
05:54 When both of the numbers have multiple digits . Thanks
05:57 for watching Math Antics and I'll see you next time
06:00 . Learn more at Math Antics dot com .
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Math Antics - Multi-Digit Multiplication Pt 1 is a free educational video by mathantics.

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