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Percents — Basic example

Watch Sal work through a basic Percents problem.

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  • marcimus pink style avatar for user snunezlichs
    , how did he end up with 20%? I don't understand why its 20%
    (15 votes)
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  • piceratops seed style avatar for user shierica sanders
    if you have questions like this how do you know if you should answer the question using these steps if there are questions worded or phrased differently
    (6 votes)
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    • female robot grace style avatar for user Sophie
      The best way you can identify a problem like this is if it assumes the starting point is 100%. Like Sal had said, if you are starting from a whole and consistently subtracting the same amount every time, you don't even need to think about the percentages, you can just substitute them as units.
      (1 vote)
  • leaf green style avatar for user Şebnem Büşra Ünver
    why did he multiplied with 0.7
    (3 votes)
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  • aqualine seed style avatar for user Sarah
    At why does Sal divide 22.40 by 28?
    (4 votes)
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  • leafers seedling style avatar for user 17jjavier
    Im having a quiz tomorrow on Ratios, Rates, Proportions, Percents and Units. Which one should i study first?
    (0 votes)
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  • leaf green style avatar for user ADITYA ROY
    As per Sal's percentage based solution, the answer should be 12.5 bcoz, when he ate 1st bowl, what was left was 92%, and after that he kept consuming 8% every time. so, here 92/8 = 11.5 ( correct ), but now we also have to add the 1st bowl which he ate. which makes (11.5 + 1) = 12.5. This is what I think. If anyone can spot any error in my judgment, please let me know.
    (4 votes)
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  • blobby green style avatar for user Haneen Dheyaa
    I didn't understand anything 😞
    (3 votes)
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  • old spice man green style avatar for user carissa.hernandez96
    where is 0.7 from?
    (3 votes)
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    • male robot hal style avatar for user Mark
      To change any decimal to a percent, you just move the decimal 2 places over to the right. With that being said, in this problem, 0.7 (or 70%) is the discounted price. How did we find out? Well the problem told us that the jeans had a 30% discount. That means you take away 30% of the original price. So you could either multiply the number (in this case $40) by 0.3 (30%) and subtract that from 40 again to get the final price of the discounted jeans, or you can do it as Sal did, which is use the rest of the percent (30% + 70% = 100%) and just multiply by 0.7 (70%) to get the discounted price without subtracting anything.
      (2 votes)
  • duskpin seed style avatar for user Preeti Kambarkar
    how did she get the 70% it doesn't mention it on there ?
    (2 votes)
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  • blobby green style avatar for user Daniel Colon
    But if the customer recieved an additional 20% from the 30%, that would be 50% off. Therefore wouldn't the total then be $20?
    (1 vote)
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    • piceratops ultimate style avatar for user Hecretary Bird
      You've just stumbled on one of the most common misconceptions about percents. If you take the percent of a percent, this is not the same as adding the percents and then multiplying it by the given value. Instead, you would have to multiply. A 20% off of a 30% would be equal to a (0.8)(0.7) = 0.56 --> 44% discount.
      (2 votes)

Video transcript

- [Instructor] We're told today, Ebuka opened a new cereal box. He ate a bowl of the cereal, which was 8% of the cereal in the entire box. Approximately how many more bowls of cereal can Ebuka expect to get from this box if he continues to eat the same amount of cereal in each bowl? All right, pause this video and see if you can answer this on your own. There are several ways that you could approach this. You could say, all right, the box starts off with 100% of the cereal. Then in that first bowl, he eats 8%, and so you're left with 92% of the original new box amount of cereal, and then every time, he's going to eat 8% of the original amount that was in the box. So if now we have 92% of the original amount in the box, and at every serving, he's going to eat 8% of it, we just divide by 8% to figure out how many servings he'd have. And so 92 divided by eight. See, eight times 11 is 88, and then you have four more, so this is going to be 11 and a half bowls, and that is this choice right over here. If the percent is confusing, you could say, all right, let's just imagine that there were, I don't know, 100, pick a unit, in the original box. Then every serving, he eats eight, and so he's left with 92 and then if every serving, he's eating eight, 92 divided by eight is 11.5.