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Relating addition and subtraction

Sal shows the relationship between 2+3=5, 5-2=3, and 5-3=2.

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  • blobby green style avatar for user MackenzieF
    2 green balls and 3 purple balls is 5 balls together
    (15 votes)
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  • duskpin ultimate style avatar for user Matthew.Arthur.Marquez
    There are 4 types of basic adding, subtracting.( I think ). There is addition+, subtraction-,multiplicationX, and dividing/. Now, if you are willing to add, you need to take the first number and add that to the second number. Then you have your answer. Subtraction is different, I you have a number, and a different number than you have got to take away the how ever many numbers from the first number of the second number. Now, multiplication is a whole new level. The way you work this type is to add the first number however many times the second number is. Dividing is harder. You have the first number and the lower second number. You have got to put in the second number until you have the first. You count however many times you put in the second number until you have the remaining first number. Than you have the answer! Your welcome! (I hope this helps)
    (19 votes)
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  • male robot johnny style avatar for user ジェイス
    Um what is a reciprocal
    (5 votes)
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    • primosaur seed style avatar for user Ian Pulizzotto
      Good question for first grade!

      A reciprocal of a number is 1 divided by that number. Taking a reciprocal can also be thought of as switching the numerator (top) and denominator (bottom) of a fraction.

      Examples:
      Because 1 is 1/1, the reciprocal of 1 is just 1.
      Since 3 is 3/1, the reciprocal of 3 is 1/3.
      The reciprocal of 4/7 is 7/4, or 1 3/4.
      Because 2 4/5 is 14/5, the reciprocal of 2 4/5 is 5/14.
      0 is the only number without a reciprocal since 1/0 is undefined.

      Note that any number (other than 0) times its reciprocal is always 1. Later on, when you study operations with fractions, you will learn that division by a number is the same as multiplication by that number's reciprocal.
      (5 votes)
  • male robot hal style avatar for user Zamriz
    Just by looking at the addition problem we can also understand the subtraction problem without writing the subtraction problem.
    (7 votes)
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  • hopper cool style avatar for user Ðustin
    Math goes on infinitely, does that mean it goes infinitely both positively and negatively? So, if it is limitless in positive numbers (above zero), then would the opposite of infinity be 'negative infinity' or simply, again, infinity?
    (3 votes)
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  • starky seedling style avatar for user NICKNAME
    101010101001010101010100101
    (3 votes)
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  • aqualine seed style avatar for user dgpro82648
    i need help with my math. {PLZ HELP!}
    (4 votes)
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  • leafers ultimate style avatar for user VictorM
    i ts easy 1,342+1,327=2,669
    (3 votes)
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  • piceratops ultimate style avatar for user T  H  A  N  O  S
    What does relation mean in this instance?
    (3 votes)
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  • old spice man green style avatar for user Leon Hook Hook
    Why was the plus symbol chosen as the plus symbol and the minus?
    (2 votes)
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Video transcript

I have two green balls and three purple balls so how many balls do I have altogether? So two green balls and three purple balls is going to be 5 balls altogether. We can count them; one, two, three, four, five. Now what if we did something a little different? Let's start with the five balls, and let's take away two. Let's subtract two of these balls. Take away one and two, and what are we left with? We are left with one, two, three balls. We're left with three balls. You might see a pattern here; two plus three is equal to five but if you start with five and take away two, you're going to be left with three. Look how they're arranged. Two plus three is equal to five and five minus two is three. It works the other way around. If I start with five and I were to take away three, if I subtract one, two, three, what am I left with? I'm left with one, two, I'm left with two. So two plus three is five, three plus two is five, which is another way of saying that five minus two is three, or five minus three is two. Take a look at this, it's a really important idea to understand in math. If you add two numbers and you get another number, then you take the result and subtract one of these you're going to get the other number.