Video transcript
Let's see if we can divide30.24 divided by 0.42. And try pausing the videoand solving it on your own before I work through it. So there is a couple ofways you can think about it. We could just write itas 30.24 divided by 0.42. But what do you do now? Well the importantrealization is, is when you're doing adivision problem like this, you will get thesame answer as long as you multiply or divide bothnumbers by the same thing. And to understand that,rewrite this division as 30.42 over 0.42. We could write itreally as a fraction. And we know that when wehave a fraction like this we're not changing thevalue of the fraction if we multiple the numeratorand the denominator by the same quantity. And so what could wemultiply this denominator by to make it a whole number? Well we can multiply itby 10 and then another 10. So we can multiply it by a 100. So lets do that. If we multiply thedenominator by 100 in order to not change thevalue of this, we also need to multiply thenumerator by 100. We are essentiallymultiplying by 100 over 100, which is just 1. So we're not changing thevalue of this fraction. Or, you could view this,this division problem. So this is going tobe 30.42 times 100. Move the decimal two placesto the right, gets you 3,042. The decimal is now thereif you care about it. And, 0.42 times 100. Once again move the decimalone, two places to the right, it is now 42. So this is going to be theexact same thing as 3,042 divided by 42. So once again we can move thedecimal here, two to the right. And if we move thattwo to the right, then we can move thistwo to the right. Or we need to movethis two to the right. And so this is where,now the decimal place is. You could view this as 3,024. Let me clear that3024 divided by 42. Let me clear that. And we know how to tacklethat already, but lets do it step by step. How many timesdoes 42 go into 3? Well it does not go at all,so we can move on to 30. How many timesdoes 42 go into 30? Well it does not go into 30so we can move on to 302. How many times does42 go into 302? And like always this is a bitof an art when your dividing by a two-digit or a multi-digitnumber, I should say. So lets think aboutit a little bit. So this is roughly 40. This is roughly 300. So how many timesdoes 40 go into 300? Well how many timesdoes 4 go into 30? Well, it looks likeit's about seven times, so I'm going to try outa 7, see if it works out. 7 times 2 is 14. 7 times 4 is 28. Plus 1 is 29. And now I can subtract. Do a little bit ofre-grouping here. So lets see, if I regroup--I take a 100 from the 300. That becomes a 200. Then our zero tens,now I have 10 tens, but I'm going to needone of those 10 tens, so that's going to be 9 tens. And I'm going togive it over here. So this is going to be a 12. 12 minus 4 is 8. 9 minus 9 is 0. 2 minus 2 is 0. So what I got leftover is less than 42, so I know that 7 isthe right number. I want to go as manytimes as possible into 302 without going over. So now lets bringdown the next digit. Lets bring downthis 4 over here. How many timesdoes 42 go into 84? Well that jumps out atyou, or hopefully it jumps-- It goes two times. 2 times 2 is 4. 2 times 4 is 8. You subtract, and wehave no remainder. So 3,042 divided by42 is the same thing as 30.42 divided by 0.42. And it's going tobe equal to 72. Actually, I didn'thave to copy and paste that, I'll just write this. This is equal to 72. Just like that.
