Chapter 9 Lesson 7 Subtract Unlike Fractions pages 651 656 MyMath

all right guys so yesterday we we did adding unlike fractions and today we are going to subtract unlike fractions so it's lot exactly almost like what we did the other day but now it's just subtraction pages are going to be 651 to 656 name staple essential question how can equivalent fractions help me add and subtract so now we got our subtraction and we need to get equivalent fractions so maybe that's getting fraction with the denominator the same on the bottom subtracting unlike fractions is very similar to adding unlike fractions as you can see right here so there's nothing really different today we have female cuban tree frog can be up to 5 12 foot long male cuban tree frog can be up to 1 4 foot long how much longer is the female cuban tree frog than the male female and then this is the male so how much longer is the female that kind of gives you hint there which one is larger fraction by you know the way they set it up here saying wait how much longer so is the female than the male so we have 5 12 minus 1 4. okay and like we did yesterday again remember or the dominant denominators have to be the same on the bottom for us to add and subtract and this time it's not so we got we have to find common lcd you know the least common denominator on the bottom or the lcms while we practice doing so that's where you do you know you skip count 4 8 12. well guess what 12. so remember said before you can just say well does 4 go into 12 yes it does so just use the as your denominator okay and then you would say oops don't do that how many what do you multiply 4 by hang on that's the bell what do you multiply the 4 by to get 12 well you do 3 so you could do this one by 3 so you can get 3 over 12. so that's how they got this 3 over 12 right here the 5 over 12 stayed the same so that's why how they got this right here and then you just simply subtract 5 minus 3 which is 2 and then the 12 stays the same always and then we have to simplify hopefully you see that these are both even we can divide both of these by the same number which is two and then that will give us one sixth so the female is one-sixth foot longer than the male okay so again you know this is the exact same as the adding so we're not really doing much different you know we're still going to go through this just in case you missed something little bit yesterday to help you understand what what it is that we're doing here on this assignment all right so jessie finished half of her homework lakshani finished four fifths of her homework what fraction more of her homework did like shawnee finished than jessie so again it gives you hint here like how much more of her homework that she finished so it gives you hint that like shawnee is the larger of the two so that's how they got the four-fifths being first because they kind of give you little hint sorry can't breathe all right so we have four-fifths minus one-half we're not using the benchmarks okay we're just diving into this we're we're just figuring this out so we're gonna write equivalent fractions to find the lcd on the bottom remember said before tell you you can multiply the bottoms together like you say 2 goes into 5. no it doesn't so you just say well 5 times 2 is 10. okay you can do that so you say both of these i'm going to use is 10. we're going to subtract them 5 times 2 equals 10 so i'm going to multiply this 4 by 2 which gives me eight two times five equals ten so need to multiply this one by five which gives me five subtract eight minus five down here which gives me three ten stays the same so three tenths right here now again if were to use the butterfly like we did yesterday remember this is where let me use different color here maybe you're seeing too much of color here so if we use the wings this is where you put the answer at remember and then down here is we're going to put that answer 4 times 2 is 8 5 times one is five five times two is ten well it's eight minus five three ten so see we get the same answer here three tenths and three tenths as we did using the butterfly method this is just shortcut guys that's shortcut to help you out it's just shortcut to help you guys work on these problems instead of having to go through this route mean this is this is the standard way that was taught right here finding the denominator common denominator and then doing the exchange this way is kind of shortcut and it works for only adding subtracting fractions that have unlike denominators all right so let's look down here at the bottom now subtract and write it in simplest form all right well always look to say well the smallest number four will fit eight yes it will so that's why we're going to use the number eight okay and then that stays the same okay four why do we multiply four by to get eight that's two so we're gonna multiply this by two so two times one is what's 3 minus 2 is 1 the 8 stays the same 1 8. pretty easy right again you cannot just subtract know some of you're going to want to be like well 5 minus 4 is 4 6 no you cannot do that because these denominators have to be the same okay so let's go ahead and do this always say the smaller number will it fit inside the six yes so i'm not going to try the butterfly with this because know that that will fit into that that stays the same two times what equals six three so one times three is three and then you subtract that you're gonna get five minus three is two and then you keep those the same can you simplify that hope you see that both of those are even and two will fit into that so you can divide both of these again by two which will give you one third one third is your answer like so this one here will four fit inside of five it will not so i'm going to try the butterfly on this one just because don't want to use too big of numbers and figured that why not right so take and do my wing right here do my wing here do my little antennas what's 5 times 4 20 put it here that's 4 times 2 eight five times one five what is eight minus five three over twenty three doesn't fit into twenty evenly because three is prime so my answer my final answer is three twentieths pretty simple right we're gonna do the same thing with this next one here because again five won't fit into six evenly so we're gonna do the butterfly with this as well so we draw our antenna draw our antenna or sorry our wings these are antennas antennas all right so what is 6 times 4 24 what's 5 times 1 5 what's 5 times 6 30 equals we're going to 24 minus 5 because this is minus we're going to get 19 over 30. can you simplify no because 19 is prime and it doesn't fit into 30 evenly so our answer is 19 30. boom okay simple as that all right for this next one look at say well the smallest is two it does fit into 8 so we're going to use the 8 for this one just makes it easy it stays the same all right so 2 times what equals 8 that's 4 so 1 times 4 is 4 subtract that we're going to get 3 because when we subtract these and then you leave that the same so 3 8. 3 is prime it doesn't fit inside of 8. this one here does 3 fit inside of 12. it sure does so we're going to use the so that stays the same all right how many times do you multiply 3 by to get 12 3 times 4 so you have 1 times 4 which is 4 all right and then you subtract and then you get 7 minus 4 equals 3 because remember you subtract these right here and then you get 12. so you have to divide both of these by the same number because know 3 fits into 12 so we're going to divide both of those by 3 which is going to give us 1 4 1 4. next up does 3 fit inside of 6 it sure does so we're going to use 6. 3 times two equals six so we need to multiply this one by two which gives us three over six and this three fit into six yes it does so we're going to divide both of these by three which is going to give us one half so our answer is one half it's the simplifying is what you guys will probably forget about and you know it just takes while to get used to that all right this one is three fit inside of ten it does not so this one i'm going to do the butterfly method with okay so i'm going to draw my my little wings like so my antennas go up here and then my bottom goes down there 10 times two is twenty three times three is nine we're gonna subtract those then what's three times ten thirty so what's 20 minus nine we get eleven over thirty 11's prime it doesn't fit into 30 so guess what eleven thirtieths we're done pretty simple okay small number two does it fit in eight yes it does so we're gonna say we're gonna use the eight or both what times two equals eight is four so four times one is four five minus four because remember we subtract is one they stay the same one eighth is our answer does 5 fit into 15 it sure does so 15 goes here 15 goes here we're still going to subtract that stays the same because it's 2 15. 5 times equals 15 that's 3 so 4 times 3 is 12. subtract these right here you're going to get 10 over 15. and then see that hey can divide both of these by 5 because they both have 0 or 5 at the end of it which gives us two thirds two thirds as our answer pretty simple if the number fits just use that number if it doesn't use the butterfly all right this fourth bit inside of six it does not so let's use the butterfly down here so we're going to draw wings again we just do like cross multiply antenna right here five times four is twenty six times three is eighteen we're going to subtract those six times four is twenty four twenty minus eighteen is two twenty fourths they're both even so can divide them both by two again which gives me one twelfth one twelfth is my answer all right now we're going to figure out obviously we're using 15 here right so we need to figure out what this top number is so we have two thirds i'm sorry we're using 15. so we got 15 for both of these all right and 3 times five equals fifteen so five times two is ten and then five times three equals fifteen so three times three is nine so it looks to me if you do ten minus nine you're gonna get one because you'll get one right here right one over 15 that's what we got there and the last one will 6 fit into 12 yes it will so we're going to use 12. that stays the same 6 times what equals it's two so we need to multiply this one by two which is two times one and then we get three over twelve because five minus two is three and we can divide both of these by three which gives us one fourth one fourth and let's look at the not the homework the back side here angie riser bike two thirds of the mile to school on friday she took shortcut so that the ride was one ninth mile shorter how long was angie's bicycle ride on friday so you're taking two thirds one day well this day she takes away ninth of it so see this and say well three fits into nine so let's use nine right this stays the same three times what equals nine three so we need to multiply this by three which gives us six then you subtract those right there it gives you five ninths all they used to half cup of vegetable to make brownies she used another one-third cup of oil to make muffins how much more oil did she use to make brownies okay so obviously the oil it says how much more did you use so that's our bigger of our fraction one-half minus one-third okay i'm going to use the butterfly on this okay that's just how am they're small numbers it's just easier this way all right so have 2 times 3 is 6. so that's going to be there right 3 times 1 is 3 2 times 1 is 2 subtract those you get 1 1 one-sixth danielle pour three-fourths gallon of water from seven eighth gallon bucket how much water is left in the bucket so the bucket is seven eighths which is gonna be the larger right and we're taking away three-fourths well does four fit in eight yeah so let's use eight as our bottom number that stays the same four times what equals the eight two so three times two is six so you subtract these right here you're gonna get one and you get eight one eighth so as said this is lot like yesterday's and the day before that i'm just mean just like yesterday it's because it's just adding and using the butterfly method just as easy using the other way that showed you on here it's just easy as well all right so didn't give you guys secret letter yesterday and need to give you two today like got little forgetful right so today's two secret letters one of them is for dog okay for dog and then the other secret letter is for rabbit okay so dnr today are your secret letters so thank you guys if you've got any questions again feel free to ask me these like i'll give you hint i'll put right here i'd probably use butterfly for that don't have to but you can this one right here would just do it the standard way like find just four fit and eight kind of thing same thing with that one standard way backside you know this is gonna be your bigger so you're gonna subtract that one away from it again this one would use the standard way wouldn't use would not use the butterfly for that one this one here you could use definitely i'd use the butterfly for that i'd use the standard method for this and most likely i'd use the butterfly for that so all right so just gives you guys little hint there so again if you have any questions come back here to see me bring your paper and have something written on your paper so can see where you need help at because that's the big thing right again feel free to ask me that's why i'm here is to answer your questions alright guys thanks for watching make sure you click subscribe