Current time:0:00Total duration:6:19
0 energy points
Video transcript
Welcome to Level 4 multiplication. Let's do some problems. Let's see, we had 235 times-- I'm going to use two different colors here, so bear with me a second. Let's say times 47. So you start a Level 4 problem just like you would normally do a Level 3 problem. We'll take that 7, and we'll multiply it by 235. So 7 times 5 is 35. 7 times 3 is 21, plus the 3 we just carried is 24. 7 times 2 is 14, plus the 2 we just carried. This is 16. So we're done with the 7. Now we have to deal with this 4. Well, since that 4 is in the tens place, we add a 0 here. You could almost view it as we're multiplying 235, not by 4, but we're multiplying it by 40, and that's why we put that 0 there. But once you put the 0 there, you can treat it just like a 4. So you say 4 times 5, well, that's 20. Let's ignore what we had from before. 4 times 3 is 12, plus the 2 we just carried, which is 14. 4 times 2 is 8, plus the 1 we just carried, so that's 9. And now we just add up everything. 5 plus 0 is 5, 4 plus 0 is 4, 6 plus 4 is 10, carry the 1, and 1 plus 9, well, that's 11. So the answer's 11,045. Let's do another problem. Let's say I had 873 times-- and I'm making these numbers up on the fly, so bear with me-- 873 times-- some high numbers-- 90-- and I'm doing them in different colors, just so you hopefully get a better understanding of what I'm trying to explain. Let's say 97. No, I just used a 7. Let's make it 98. So just like we did before, we go to the ones place first, and that's where that 8 is, and we multiply that 8 times 873. So 8 times 3 is 24, carry the 2. 8 times 7 is 56, plus 2 is 58, carry the 5. 8 times 8 is 64, plus the 5 we just carried. That's 69. We're done with the 8. Now we have to multiply the 9, or we could just do it as we're multiplying 873 by 90. But multiplying something by 90 is just the same thing as multiplying something by 9 and then adding a 0 at the end, so that's why I put a 0 here. Let's say 9 times 3-- well, first, just to clean up things, let's get rid of what we had from before. We say 9 times 3 is 27, carry the 2. 9 times 7 is 63, plus the 2 that we just carried is 65. Carry the 6. 8 times 8 is 72, plus the 6 we just carried. That's 78. And now we just add again. 4, 8 plus 7 is 15, 1 plus 9 plus 5 is 15, 1 plus 6 plus 8 is also 15, and 1 plus 7, that's 8. So the answer, hopefully-- I don't have a calculator in front of me-- is 85,554, assuming I didn't make any careless mistakes. Let's do one more problem. I think it'll hit the point home. The next problem I'm going to do, you can almost do it as a Level 5 problem because I'm actually going to multiply two three-digit numbers, but it's really the same thing, and hopefully, you'll see the pattern. So let's say I had 234 times-- and I'm going to use three colors now-- let's say 643. So first we do the 3, which is in the ones place, and we multiply that times 234. Well, 3 times 4 is 12, carry the 1. 3 times 3 is 9, add the 1. That's 10, carry the 1. 3 times 2 is 6, plus 1. Well, that's 7. And then we've done the-- I think I've made a mistake someplace. Let me see. 3 times 4 is 12. Oh, no, I think that's correct. I was confusing myself. OK, now we're ready to do the 4, or the 40, and since it's a 40 because it's in the tens place, we put a 0 right here. We say 4 times 4-- well, let's clean up this stuff at the top. I always forget to do that. 4 times 4, well, that's 16, carry the 1. 4 times 3, well, that's 12, plus 1, well, that's 13. 4 times 2 is 8, plus the 1, well, that's 9. And now we're done with the 4, or the 40, depending on how you want to view it. Now we're ready for the 6, or the 600. Since it's a 600, we put two zeroes here, and we just treat it like a 6. Let's clean up what we did before. So 6 times 4 is 24, carry the 2. 6 times 3 is 18, plus 2 is 20, carry the 2. 6 times 2 is 12, plus 2 is 14. And now we add it all up. 2, 6, 7 plus 3 is 10. 14, carry the 1. 1 plus 9 is 10, carry the 1. That's 5. That's 1. I hope you can see. I hope it's not falling off the screen, the answer I get is a 150,462. I think you're ready now to try Level 4 multiplication problems.