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Multiplication word problem: carrots

Created by Sal Khan.

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  • male robot hal style avatar for user Naveen Hegde
    At Isn't it Same as finding Area ?
    What if we had 1 carrot in 1st row 2 carrots in 2nd ................ n carrots in nth row Then what is Total number of carrots ? is there a General Formula ?
    (30 votes)
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    • mr pants teal style avatar for user Ernest Belicic
      The problem you described is this.. how much is 1 + 2 + 3 + 4 + 5 + ... + n and there is a formula that gives you the answer n*(n+1) / 2. The reason this is true is because you can always couple the smallest and largest numbers and get some constant (the constant is always n+1).. an example:

      1 + 2 + 3 + 4 + 5 + 6 + 7 + 8
      1 + 8 = 9
      2 + 7 = 9
      3 + 6 = 9
      4 + 5 = 9

      So because you couple numbers you get n/2 pairs so to add all of them up we just have to multiply n/2 * constant = n/2 * (n+1) = n*(n+1)/2. I used an example where n is even, but it also works with odd n.
      (48 votes)
  • starky sapling style avatar for user Arman baghdasaryan
    I'M new here can someone please help me
    (4 votes)
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  • blobby green style avatar for user shaniamcclain2013
    how did you do that
    (3 votes)
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  • piceratops seedling style avatar for user tmjackson0811
    there are 1,760 yards in one mile. about how many miles will a runner have to run before seeing both a water station and trail maker at the same location? calculate the answer to the nearest hundredth of a mile.
    (2 votes)
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  • winston baby style avatar for user Julie Vayner
    i need help doing multpication b
    (2 votes)
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  • blobby green style avatar for user jason.meyer
    what is 0 over 3 divided by 78965 plus o divided by 9876
    (2 votes)
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  • aqualine sapling style avatar for user Makayla
    how do you compare with mutipcation.
    (2 votes)
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  • aqualine ultimate style avatar for user iiPlayMinecraft
    To be honest I think that is fall under area
    (2 votes)
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  • leaf green style avatar for user John
    the product of 7 and a number is 4 more than 38. find the number
    (3 votes)
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  • blobby green style avatar for user ahohvea
    At the zoo, there were 3 times as many monkeys as lions. Tom counted a total of 24 monkeys and lions. How many monkeys were there?
    (2 votes)
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Video transcript

Toby is a farmer. He plants 12 rows of carrots in a field. Each row has 6 carrots. How many carrots did Toby plant? So let's try to visualize this thing. So they tell us each row has 6 carrots. So let's try to visualize a row. So that's 1 carrot, that's 2 carrots, that's 3 carrots, that's 4 carrots, that's 5 carrots, and that's 6 carrots. And I can even do, just so it looks nice, the little leafy part of the carrots. So we can visualize these as carrots. So that's 1 row of carrots. They tell us each row has 6 carrots. Now, there're 12 of these. He plants 12 rows of carrots. Let me see if I can copy and paste this. So copy and paste. So that's 2 rows. I want to make sure I have enough space. 2 rows. That's 3 rows. That's 4 rows. This is 5 rows. This is 6 rows. And actually, I can just copy and paste the whole thing. This is 6 rows. I just need to double that to get to 12 rows. So let me do that. So copy and paste. There you go. So there's 12 rows right over here. And let's number this. So they tell us each row has 6 carrots-- 1, 2, 3, 4, 5, 6. They tell us he plants a total of 12 rows-- 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12. How many carrots did Toby plant? Well, you could do this exercise and then try to count all of these carrots. But that seems a little bit crazy. These are already a lot of carrots. And especially if these were even larger numbers, it would take you forever to count it. Luckily for us, we have multiplication as a tool that we can use. So if you have 12 rows and each of those rows have 6, this is really 12 times 6. You're going to have 12 rows. In each of those, you have 6 carrots. So you could say you have 6 carrots 12 times. So it's going to be 12 times 6. If you remember your multiplication tables up to 12, you'll remember that 12 times 6 is 72. So he has 72 carrots. Even if you only remember-- well, I'll just leave it there. If you remember your multiplication-- which you should, because that is one of the things in life that will have long-lasting benefits-- it's 72 carrots.