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Video transcript

let's say I go to the fruit store today and they have a sale on guavas everything is 30% off this is for guavas on guavas and it's only today only only today so I say you know what let me go buy a bunch of guavas so I go and I buy 6 guavas so I buy 6 guavas and it ends up when I go to the register and you know we're assuming no tax for you know it's a grocery and I live in a state where they don't tax groceries so for the 6 guavas they charge me I get the 30% off they charge me $12.60 twelve dollars and sixty cents so this is the thirty percent off sale price on six koalas I go home and then my wife tells me you know Sal can you go get two more guavas tomorrow I say sure so the next day I go and I want to buy two more guavas so two guavas but now the sale is off there's no more 30% that was only that first day that I bought the six so how much are those two guavas going to cost me how much are those two guava is going to cost at full price at full price so a good place to start is to think about how much what are those six guavas cost us at full price this is the sale price right here this is the sale price how much would those have cost me at full price so let's do a little bit of algebra here let me pick a suitable color for the algebra oh maybe this is a grey color so let's say that X is equal to the cost of 6 guavas 6 guavas at full price so essentially if we take 30% off of this we should get $12 and 60 so let's do that so if we have the full price of 6 guavas we're going to take 30% off of that so that's the same thing as 0.30 or I could just write point 3 I could ignore that 0 if I like actually let me write it like this my wife is always bugging me to write Rose before decimals so that's the full price of 6 guavas minus 0.30 times the full price of guavas so I'm literally just taking 30% off of the full price off of the full price this is what how we figure out the sale price this is going to be equal to that 12.6 tea right there that's going to be equal to 12 dollars and 60 I just took 30% off of the full price and now we just do algebra we could imagine there's a 1 in front you know X is the same thing as 1x so 1x minus 0.3 X is going to be equal to 0.7 X so we get 0.7 X we can say 0.7 if you like same number point or 0.7 X is equal to 1260 and once you get used to these problems you might just skip straight to this step right here well you say a 70% of the full price is equal to my sale price right I took 30% off this is 70% of the full price you might just skip to this step once you get used to these problems a little bit and now we just have to solve for X divide both sides by 0.7 so you get X is equal to 12 60 divided by 0.7 we could use a calculator but it's always good to get a little bit of practice dividing decimals so let's do that so we get zero point seven goes into 12 60 let's multiply both of these numbers by 10 which is what we do when we move both of their decimals one to the right so the point seven becomes a 7 ignore that right there the the 1260 becomes 126 put the decimal right there a decimal right there and we're ready to just do straight-up long division so this is now a 7 not a point 7 so 7 goes into 12 one time 1 times 7 is 7 12 minus 7 is 5 bring down the 6 7 goes into 56 8 times 8 times 7 is 56 and then we have no remainder so it's 18 and there's nothing behind the decimal point so it's 18 in our case $18 so X is equal to $18 remember what X was X was the full price of 6 out of 6 guavas X was the full price of 6 did I say avocados X is the full price of 6 koalas now the question is how much will two guavas cost me the full price well this is full full price of 6 so you immediately could figure out what's the full price of one guava you divide 18 by 6 so 18 divided by 6 is $3 that's $3 per guava at full price and they're asking us we want to guavas so 2 guavas is going to be 2 times $3 so this is going to be six dollars six dollars another way you could have done it you could have just said hey 6 at full price you're going to cost me $18 two is one third of six so one third of $18 is $6 so just to give it a quick review of what we did we said the sale price on six koalas $12 sixty that's 30 percent off the full price or you could say this is 70 percent of the full price 70 percent of the full price and so you could say 30 percent so if you say X is the full price of 6 guavas you could say the full price of 6 guavas minus 30 percent of the full price of 6 guavas is equal to 12 60 and that's equivalent to saying 70 percent of the full price is 1260 you divided and we just solve this algebraically divide both sides by 0.7 and then we got X the full price of 6 guavas is $18 or that's $3 per guava or $6 for 2 anyway hopefully you found that helpful