Multiplying 4-digit by 1-digit (regrouping)

let's multiply 9 times 8,000 8085 that should be a pretty fun little calculation to do so like always let's just rewrite this so I'm going to write the 8085 I'm going to write the 9 right below it and write our little multiplication symbol and now we're ready to compute so first we can tackle 9 times 5 well we know that 9 times 5 is 45 we can write the 5 in the ones place and carry the 4 to the tens place so 9 times 5 is 45 now we're ready to move on to 9 times 8 we're going to calculate 9 times 8 and then add the 4 that we just carried so 9 times 8 is 72 plus the 4 is 76 so we'll write the 6 right here in the tens place and carry the 7 now we are ready to calculate and I'm looking for a suitable color 9 times 0 9 times 0 hundreds plus and this is a 7 in the hundreds place so that's actually 700 or if we're just kind of going with the computation 9 times 0 plus 7 well 9 times 0 is 0 plus 7 is 7 is 7 and then finally finally we have and once again I'm looking for a suitable color 9 times 8 9 times 8 this is the last thing we have to compute we already know that 9 times 8 is 72 and we just write the 72 right down here and we're done 8,000 85 times 9 is 72 thousand seven hundred and sixty-five let's do one more example just to make sure that this is really clear in your brain at least the process for doing this and I also want you to think about why this works so let's try let's try 7 times 5 thousand five thousand three hundred and ninety-six and encourage you to pause it and try it on your own as well well five thousand I'm going to rewrite it five thousand three hundred ninety six times seven first we'll think about first we'll think about what seven times six is we know that's 42 put the two in the ones place for we will carry then we need to concern ourselves with seven times nine but then we have to calculate that and then add the four 7 times 9 is 63 plus 4 is 67 so we get we put the 7 down here and carry the 6 then we have to worry about 7 times 3 plus this 6 that we had just finished carrying 7 times 3 is 21 plus 6 is 27 so we'll write the 7 here the hundreds place and carry the 2 and then finally we have 7 times 5 which is 35 but we have to add the two 35 plus 2 is 37 so 5 thousand three hundred ninety six times seven is 37 thousand seven hundred and seventy-two