Early math review
Adding 7 + 6
Sal adds 7 + 6 using the number line. Created by Sal Khan.
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- Why are number lines used? Isn't the adding or taking objects away thing easier than a number line?(21 votes)
- You will need to know numbers lines later on, when you start geometry with points, lines, curves and vectors.
Also, numbers lines can be more useful than objects when it comes to:
* Negative numbers
* Large numbers (think thousands)
* Decimal numbers (1.623, 76.8).
* Skip counting(27 votes)
- what are percentages? how do we calculate them? how do turn fractions into them? what is the origin of percentages? how will they help in life(12 votes)
- Percentages are parts of a hundred- 'per' 'cent'. 'Cent' means one hundred like century or centimeters. We calculate them by cross multiplying x over one hundred and another fraction. We can turn fractions into percentages by cross multiplying it with x over one hundred. I'm not sure of the origin- I'm sure you can find it if you Google it- and they help in life because we can see how much of one hundred is being used.(12 votes)
- what is randing(7 votes)
- Rounding is when you look to the guy next door. For example, if you are rounding 18 to the nearest tens place, look at the number next to the ten. If it is five or more, make the number next to the one a 0 and the tens place a 2 (add 1 to the tens place) if it is less than five, turn all of the numbers next to the tens place into zeros.(7 votes)
- what are cube roots and square roots? how they calculated? what is the point of it? who created it? is there an easier way of calculating these numbers? is there an easier way of saying 13 to the 5th power? Thanks for answering! :)(7 votes)
- Hey, Tim! Square roots are a number multiplied by itself to get another number. For example, 144 squared is 12 since 12 * 12 = 144. Cubed roots are like square roots, except instead of times itself, it would be the number multiplied by itself three times. For example, 27 cubed is 3 since 3 * 3 is 9, and 9 * 3 = 27. Hope this helped :)(4 votes)
- what are negative numbers? how do we add, subtract, multiply, and divide them? also when we multiply negative numbers why does it turn positive(7 votes)
- Negative numbers you usually cover in 6th grade. They're basically and number less than zero, or to the left or zero on a number line. Hope this helps!(3 votes)
- so when ever you add a even nuber and a odd number you will get a odd?(6 votes)
- Like Sabbarish's answer stated, you can use that method to remember if the results odd or even.
To remember it better, think of the even numbers as couples. If you put odd and even together, the odd one's going to stand out since it doesn't have a partner.
Likewise, if you put two odd numbers together, the numbers can become a "couple", creating an even number.(5 votes)
- why aren't there subtitles?(4 votes)
- Many Khan Academy videos have subtitles; click the
CCbutton in the bottom right corner of the video to access them. Alternatively, you could use the interactive transcript (click the
Transcriptbutton right next to
- i need help to do that beacuse i am slow(4 votes)
- how many 1 are in 7? and how many 1 are in 6?
7 is 1+1+1+1+1+1+1
6 is 1+1+1+1+1+1
So when you put those 2 together, because you are adding, you will get:
So if you wanted to count those, you will say:
1, then 2, then 3, then 4, then 5, then 6, then 7, then 8, then 9, then 10, then 11, then 12, then 
1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1
So there it is, you counted all the ones you had until you reached the number 13
Hope that answers your question.(2 votes)
- Hey, I'm curious to know if someone wants to answer my question.
Can someone tell me all the possibilities (of additions) to make 13?(3 votes)
- It's a long progress to find out. Think of all the numbers in between. There are so many numbers you can add together to make 13(2 votes)
- I am curious at to why you don't also include a list of Math Addition Facts (or Subtraction, Multiplication & Division Facts)
I understand Why you teach it this way, but, once we understand why and how things are done, wouldn't it be a great supplement and simpler to memorize the Addition Facts for 7 (and all the other Number up to 9 or 12)?
So My sub Question -
Is it Ok to Memorize Math Addition Facts After You Understand what Addition is to make things go faster in the end?
Is it Ok to do the Same for Subtraction, Multiplication & Division also?(4 votes)
- i dont know what you guys are talking about but is really weird stuff i say weird stuff to(0 votes)
Voiceover:Let's think about what seven plus six is, and I encourage you to pause this video and think about it on your own. I'm assuming you've given a go at it. Let's think about it. We could do this as seven objects plus six more objects, and then think about how many total objects we had. For example, we could view it as seven, say, tomatoes, so one tomato, two tomatoes, three tomatoes, four tomatoes, five, six, and seven, and then to that, we're going to add six more objects. Let's say they're blueberries, and we care about the total amount of fruit. So, one, two, three, four, five, and six - six blueberries. Now, how many total pieces of fruit do I have in all now? I started with seven, so that's seven. If I keep counting, this is seven so this is going to be eight, nine, 10, 11, 12 and 13. I now have a total of 13 pieces of fruit - 13 pieces of fruit. What are other ways that we could have thought about this? We could have also done it on a number line. Let's draw ourselves a number line. Let me do this in a color that I haven't used yet, actually. Let's say I have a number line just like that. I can start the number line at seven. I could start at seven, and I'm going to add six more. I'm going to move six more up the number line. This is one, two, three, four, five, six, and, of course, I could keep going. It's going to be eight, nine, 10, 11, 12, 13. Of course, you could keep on going. Seven plus six - you could visualize this as starting at seven, and then making six jumps up the number line - one, two, three, four, five, six. Either way, we get to 13. Another way to think about it is, look, we started with seven. We added three to get to 10, and so we have to add another three, which gets us to 13. That really goes to the heart of what the number 13 represents. The number 13 has a one as its left digit, This digit is in the tens place, so it literally represents one 10. So, it's one 10 plus three, plus three ones. You see that right over here. When I added the pieces of fruit, this right over here is one group of 10. So, that's one group of 10. We had to add three to get to that one group of 10. We kind of filled that bucket, and then we had three more, so when you add seven plus six, you fill one whole group of 10 and then you have three ones left over. This is the three ones right over here. Another way you could think about it is seven plus six is the same thing as 10 plus three, which, of course, is 13. This is the same thing - one 10 is 10, plus three, plus three ones - 13 either way you look at it.