Multiply Fractions Lesson 2-Making Cookies

everybody um this should be multiplyingfractions lesson number two um and we’rejust gonna dive right in here um so herewe have a recipe for chocolate chipcookies and if you’re like me hopefullyyou’ve done some baking during this timebut here’s a recipe for chocolate chipcookies and as you can see we need oneand a half cups of margarine this bigsee sings four cups sorry 1 and 3/4 cupsof sugar this tea the big T stands fortablespoon so we need two tablespoons ofvanilla 3 and 1/4 cup of flour 1 thislittle T is teaspoon so one teaspoon ofbaking powder 1/4 of a teaspoon of saltand eight ounces of chocolate chips sothis first question we’re gonna answeris question a it says how much of eachingredient is needed to make threebatches so this is the recipe for onebatch of cookies now what we want toknow is how much do we need of eachingredient if we’re making three of themso let’s let’s start right at thebeginning here with this one in 1/2 cupof margarine so I know that I need oneand a half cups of margarine for onebatch and I want to know what do I needfor three batches now there’s a coupledifferent ways that you could start bydoing this I’m gonna start with repeatedaddition because that’s we’re in mybrain way my brain said well I know thatif I have one and a half for this batchthen for batch two I would need one in1/2 and four backs three I would needanother one in 1/2 so one in 1/2 + 1 and1/2plus one and one hats now my brainstarts with a fraction part of it if youwant to add the whole numbers first itdoesn’t change anything but I’m gonnastart with the fractions here and whenI’m looking I know that when I add orsubtract fractions I need to make surethat my denominator or my bottom numberis all the same value so here they’reall the two so they’re all the same so Ican just add straight with my numeratorsso I have one plus one plus one which isgonna be three and my denominator willnot change then I go through and I addmy whole numbers one one and one whichwould get me three so I have three andthree halves now if you’re looking atthis in your go on some just looks kindof funky about this I’m not quite surewhat I’m supposed to do here here’s whatyou do you look at the numerator and thedenominator since your numerator isbigger than your denominator that meansyou can pull out a whole number here soif I were to draw three over two thatmeans I have three pieces of two orhalves so here’s one piece here’s topeace oh I need another one that’s threeso how many holes do I have here I haveone hole in one out of these two piecesso 3 plus 1 and 1/2 would now be 4 and1/2 so I need 4 and a half cups ofmargarineanother way that you could have solvedthis is using that multiplication so youknow that repeated addition here 1 and1/2 plus 1 and 1/2 plus 1 and 1/2 isreally gonna be the same as 1 and 1/2multiplied by 3 now if you’re gonna doit this way which againtotes fine is you’re gonna have tochange this here into an improperfraction or a fraction greater than 1and the way that you do that is you saythat 2 times 1 is 2 plus 1 would be 3let’s walk through that again that waskind of fast 2 times 1 so yourdenominator times your whole number ormultiplied by your home lumber andyou’re gonna add your numerator sothat’s 3 over 2 multiplied by 3 andwe’re gonna make that look the same wayso 3 times 3 is 9 2 times 1 is 2 then wesay again hmm this looks weird to melook if you can even see it sorrythis looks a little weird to me cuz mynumerator MINDEF my top number is biggerthan my bottom number here so you gookay how many times or how many twos fitinto the number 9 so you go okay well 24 6 8 right so I can’t get four twosinto the number 9 how many would be leftover one out of how many whatever yourdenominator is which would be 2 hey ouranswers match if you are ever unsure orin all honesty what I would do is Iwould do both of these the repeatedaddition and the multiplication to makesure that my answers match if youranswers don’t match then you’re gonnahave to go back and go oh shootsomewhere I made no right okay that isfor Part A what you need to do is youneed to do the rest of them on your ownbut I’m gonna do I’m gonna jump to B sothat you can see an example of what Blooks likewe have to move this down okay so we’rejumping to B so it says how much of eachingredient is needed to make 3/4 of arecipe so before we were making morethan what this recipe called for rightwe had to make three different groups ofthis what we’re doing now is we’remaking it into a smaller batch so I’mgonna do the same thing with themargarine again so one batch is 100 1/2cups and I’m just gonna put large thistime I need to know how much I need for3/4 of a batch so it wants 3/4 of 1 and1/2 so you actually are going tomultiply I know miles playing fractiongets a little tricky because we’re soused to when we multiply something thatit gets bigger but with fractions it’sactually the opposite you okay so we hadone 3/4 of which means to multiply inthis case one in 1/2 and it’s the sameprocess kind of as before so I’m gonnajump over here to where up some room towork here so I want 3/4 I’m gonnamultiply that by one and 1/2now when you’re multiplying this by orwhen you go to multiply this you’regonna want to again change it into thatfraction greater than one or thatimproper fractionlucky duck for us we’ve already done itbut I’ll walk you through it again ofhow to do it so you take yourdenominator times your whole numberwhich is 2 times 1 which would be 2 andyou’re gonna add 1 which would give you3 okay then you just multiply acrosslike you would 3 times 3 is 9 4 times 2is 8 so I have 9 8 now again you shouldlook at this and you should say Ohsomething looks a little wonky donkeyhere 9 my numerator is bigger than 8 mydenominator which again means thatthere’s a whole number in there that Ican pull out if you want to draw it outand your brain works works better seeingit drawn out please do whatever worksbest for your brainbut I’m gonna ask the question here howmany eighths can you get into nine theanswer would be who can get one eight intonight how many pieces would be leftover if I took eight pieces and put theminto nine how many would be left therewould be one piece out of how many eightso how many cups of margarine do youneed you want three fourths of a batchyou need one and 1/8 cups of margarinenow let’s think about this for a seconddoes this answer make sense so we haveto stop and ask ourselves becausesometimes for an emitter and math wejust keep going we get going and wedon’t even stop to think right now let’sstop and think here for one batch I needone and a half if I’m making 3/4 of abatch that means I’m making less thanone whole of the batch right I’m notmaking the full thing I’m just makingthree-fourths so what I need more orless margarine in the 3/4 I would needless because I’m making smaller thanwhat is actually called for so is one in1/8 smaller than 1 and 1/2 yeah so ouranswer here would make sense perfectagain so hopefully you’ve gone back andnow or you’re about to go back and dothe rest of a with the rest of theingredients and then I want you to dothe same thing with B so you’re gonna goback with the ingredients and you’regonna do the rest of the ingredientswith only making three-fourths of thatrecipe awesome stuffOh that’ll make sense you’re awesomekeep up the great work