Welcome to level four multiplication let's do some problems.
Let say we had 235 x 47, so you start at level four problems just like you would normally do a level three problem, so we take that 7 and we multiply it by 235. So 7 x 5 is 35, 7 x 3 is 21 plus the 3 we just carried that’s 24, 7 x 2 is 14 plus the 2 we just carried this is 16. So we’re done with the 7 now we have deal with this 4. Well since that 4 is in the tens place we add the zero here. You could almost view it as we’re multiplying 235 not by four but we’re multiplying it by 40 and that’s what we put that zero there.
But once you put the zero there you can treat it just like a four. So you say 4 x 5 well that 20 let's ignore what we had from before, 4 x 3 is 12 plus the 2 we just carried which is 14, 4 x 2 is 8 plus the 1 we just carried so that’s 9 and now we just add up everything 5 + 0 is 5, 4 + 0 is 4, 6 + 4 is 10 carry the one, 1 + 1 + 9 that’s 11 so the answer is 11045.
Let's do another problem. Let say I had 873 times and I'm making this numbers up on applied so bare with me. 873 x 90 and I'm doing it on different colors just so you hopefully you get a better understanding of what I'm trying to explain. Let say 97, no I just used the 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 x 873. So 8 x 3 is 24 carry the 2, 8 x 7 is 56 + 2 is 58 carry the five, 8 x 8 is 64 + 5 we just carried that’s 69. We’re done with the 8 and now we have to multiply the 9 and where can just use is 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 zero at the end. So that’s why put a zero right here and say 9 x 3 but first just to clean up things let's get rid of what we had from before. We say 9 x 3 is 27 carry the 2, 9 x 7 is 63 + the 2 that we just carried is 65 carry the 6, 9 x 8 is 72 + the 6 we just carried that 78 and now we just add again 4, 8 + 7 is 15, 1 + 9 + 5 is 15, 1 + 6 + 8 is also 15 and 1 + 7 that’s 8 so the answer hopefully I don’t have a calculator in front of me that 85554 assuming I didn’t make any careless mistakes.
Let's do one more problem I'll think it will hit the point home. The next problem I'm going to do you can almost do at the level five problems 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 say I had 234 x 643, so first we do the three which is in ones place and we say we multiply that times 234. Well, 3 x 4 is 12 carry 1, 3 x 3 is 9 add the 1 is 10 carry 1, 3 x 2 is 6 + 1 that 7 and then we've done the—I think I've made a mistakes some place, let me see.
I was confusing myself. Okay, now we’re ready to do the 4 or the 40 and since it a 40 because in the tens place we put a zero right here. Let say 4 x 4 that’s 16 carry the 1, 4 x 3 that’s 12 + 1 that’s 13, 4 x 2 is 8 plus the 1 well its 9 and now we’re done with the 4 or the 40 depending on how you want to do it. Now we’re ready for the 6 or the 600. Since it’s the 600 we put two zeros here and we just treat it like a 6. So 6 x 4 is 24 carry the 2, 6 x 3 is 18 + 2 is 20 carry the two, 6 x 2 is 12 + 2 is 14 and now we added all up. I hope you can see that, I hope this falling off to the screen. But the answer I get is 150,462. I think you're ready now to try a level four multiplication problems.
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