2-Digit Multiplication: A Step-By-Step Review | Multiplying by a 2-Digit Number | Math with Mr. J

[Music] welcome to math with mr j [Music] in this video i'm going to go through a quick review of two digit multiplication if it's been a while and you need a quick refresher this should be helpful whether you're in high school college continuing your education as an adult helping with an assignment or maybe you just learned this recently and need a quick refresher really no matter where you're at here are a couple of examples to help you out let's jump into number one where we have 48 times 23. now the first thing that we need to do we need to line this up vertically so we're going to rewrite it up and down let's go below the problem here and we have 48 times 23 so once we have that rewritten vertically we need to multiply the top number by the ones digit of the bottom number so the ones digit of the bottom number is the 3 in 23 so we need to do 3 times 8 and then 3 times 4. we can forget about the 2 and 23 right now we're just worried about the ones place so let's start with 3 times 8 which is 24 so we'll write our 4 and then carry the 2. then we take that 3 and multiply it by the 4 and 48 so we're moving to the left to the tens place of that top number so 3 times 4 is 12 plus the carry 2 is 14. so we can write our 4 and then the carried one well there aren't any more places to the left so we can just bring it straight down and we end up with 144 so we are done with that three in the ones place i'm going to cross it off and we are done with that carried two i'm going to cross that off as well that way we know we're done with that 3 and the carry 2 and we can move forward so our next step we're going to multiply the top number by the tens digit of the bottom number so the 2 from 23 now we do need a 0 since we are moving over to the tens place and that 2 has a value of 20. so we need to make sure we write a 0 here again because we're moving over to the tens place and that two has a value of twenty once we have that zero we can do two times eight and then two times four two times eight is sixteen so we write our six and then carry our one now we can do two times four plus that carried one two times four is eight plus the carried one is nine so we end up with 144 and 960 there once we get to this point we add so let's add these two numbers together and those are called partial products they're part of our final product now we're ready to add and we're going to start with the ones place so we have four plus zero that's four then we move to the tens place we have four plus six which is ten so we can write our zero and then carry our one and then for the hundreds place we have one plus one plus nine so one plus one is two plus nine is eleven so we can put our one here and then we carry a one over to the thousands place and it's all by itself so we can bring it straight down and we end up with 1104 and that's our final answer now one more thing i do want to mention before moving on and this is going to help us understand what we're doing within this problem so we started by multiplying the top number by the ones digit of the bottom number so we did 3 times 48 there 3 times 48 and that equals 144 which we have right here then we move over to the tens digit and multiply that by 48 and that tens digit is a 2 but it has a value of 20 because it's in the tens place so we did 20 times 48 as well and that equals 960 which is right here and then we add those together to get the final product let's move on to number two where we have 849 times 75 remember the first thing that we need to do we need to line this up vertically so up and down we have 849 times 75 let's start with the ones place of that bottom number and multiply it by the top number so we'll start with 5 times 9 which is 45 let's put our 5 carry the 4. then we have 5 times 4 we're moving over to the tens place now in that top number 5 times 4 is 20 plus 4 is 24 carry the 2 and then we end with the hundreds place of the top number so let's take our ones place from the bottom number that 5 times the hundreds place of the top number 5 times 8 is 40 plus that 2 is 42. so we'll put our 2 and then no more places to the left so we can just bring that 4 straight down so we are done with the ones place now we did 5 times 849 and we got 4245. i can put a comma in here we're done with this five and then this carried four and this carried two so now we're going to move over to the tens place of that bottom number and multiply that by the top number so we have a seven in the tens place now again we're in the tens place here so that has a value of 70 so we need our zero now we can multiply we'll start with seven times nine which is sixty-three carry that six seven times four is twenty-eight plus six is thirty-four put our four carry the 3 and now we have 7 times 8 which is 56 plus that 3 is 59. so we put our 9 and then our carried 5 we don't have any more places to the left so we can bring that straight down put our comma and now we're ready to add so to recap 5 times 849 is 4245 and then 70 times 849 is 59 430. at this point we are ready to add our partial products to get our final product which is the answer to a multiplication problem let's start with the ones place and work our way left so five plus zero is five four plus three is seven two plus four is six four plus nine is 13 so a 3 there and then carry the 1 and then 1 plus 5 is 6. put our comma in and our final answer is 63 675 so there you have it there's a quick review of two-digit multiplication i hope that helped thanks so much for watching until next time peace you