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Current time:0:00Total duration:5:12

Ratios on coordinate plane

CCSS.Math: ,

Video transcript

we are told that a baker uses 8 cups of flour to make one batch of muffins for his bakery complete the table for the given ratio so they're saying that for every batch he needs 8 cups or flour or he needs 8 cups of flour for every batch so if he had 2 batches how many cups of flour would that be pause the video and try to figure it out well if he has twice as many batches he's gonna have twice the number of cups of flour so instead of 8 it would be 16 cups of flour and if he had 3 times the number of batches it would be 3 times the number of cups of flour so instead of 8 it would be 8 times 3 or 24 now down here they say plot the ordered pairs X comma Y from the table on the following graph so we want to graph one batch 8 cups 2 batches 16 cups 3 batches 24 cups so let's do that so let's see if you can ok so right here I'm assuming on the horizontal axis that is our batches and then on our vertical axis is cups of flour so for every batch we need 8 cups of flour so one batch this is 8 right over here 5 6 7 8 and then for 2 batches we're going to need 16 cups of flour so that puts us right over there that's 16 and then for 3 batches we are going to need 24 cups of flour and that actually goes slightly off of our screen here let me scroll up a little bit so for 3 batches we are going to have to bring that to 24 which is right here and I can see the 25 right above that and what you'll see because the ratio between our batches and our cups of flour are constant that all of these points you could connect them all with one straight line because we have a fixed ratio every time we move one to the right we're going to move 8 up every time we add another batch we're gonna have 8 more cups of flour every time we add a batch 8 more cups of flour let's do another example here we're told drew or money washing cars for his neighbors on the weekends drew charges a set rate for each car he washes the points on the following coordinate plane show how much drew charges four to five and eight cars let's see what's going on over here so when he washed his two cars he looks like he charges fifteen dollars when he washes five cars it looks like he's charging well it looks like someplace between 35 and 40 dollars and we charges eight cars it looks like he's charging sixty dollars so one way to think about it is the ratio between the number of cars he's washing and the dollars it stays at to 215 notice two cars for every 15 dollars I guess I could say fifteen dollars for every two cars and so when you go to eight cars you're multiplying by for the number of cars and you're also multiplying by for the number of dollars and so once again since we have a fixed ratio here all three of these points sit on the same line but then they ask us down here they say how much does Drew charge for four cars well if it's fifteen dollars for two cars well then four cars would be twice as much so it would be thirty dollars for four cars we have the same ratio let's do one more example here we're told McKenna earns money each time she shovel snow for her neighbors as she should McKenna plots points on the coordinate plane below to show how much she earns four different numbers of times she such levels snow all right so let's see when she stubbles snow three times looks like she gets see halfway between 16 and 20 looks like she gets $18 four times okay it's $24 so it looks like the ratio is staying constant at 3 to 18 the ratio of 3 to 18 is the same thing as or one way to think about it is $18 for every three times she sells snow that would be equivalent $6 for every time she shovels snow so let's go down here to see what they're asking us they say which of the following ordered pairs could McKenna add two Graff so this would be one time so shoveling snow which you get $10 for it so does she get $10 for every time she shovels snow no that wouldn't be consistent with the data here she got $18 for shoveling snow three times so that looks like she's getting six dollars for every time she shovels the snow so I would rule out choice a choice B shoveling snow twice she gets $12 well that makes sense if she gets six dollars every time she shovels snow if the ratio of shoveling of the times to the dollars is three to eighteen or one to six that would be equivalent to two to twelve and we would pick that choice