ShmoopTube

00:03

Long Multiplication, a la Shmoop.

00:06

Ah, the holidays. A time to come together… [Christmas tree and presents]

00:09

…to wage war over politics and tell the kids their life choices are disappointing.

00:16

It’s no different for the Rabbit family, who are preparing their annual Bunsgiving feast.

00:21

Jack and Bunny Rabbit have an insane number of kids and grandkids. [Jack and Bunny with their kids]

00:25

But it’s always a chore figuring out how much carroturkey to cook for so many hungry tummies.

00:31

The Rabbits have 49 children, and there are 37 grandchildren per child.

00:36

How many total children and grandchildren are there? [Maths long multiplication problem]

00:40

To solve a problem like this, you’ll need to use long multiplication. [Students working in class]

00:44

Don’t be deceived by the name though.

00:46

In fact, it’s actually a bit of a shortcut.

00:48

Rather than adding up the grandkids for all 49 children…

00:52

…long multiplication will allow us to quickly determine the total number of mouths there are to feed. [Bunny chewing food]

00:57

When else might you need to use long multiplication?

01:00

Suppose you have 15 people to buy Christmas presents for, and you plan to spend $25 on each person.

01:05

Long multiplication will be handy for figuring out how big a dent this is going [Girl using a calculator]

01:09

to put in your checking account.

01:11

All right, so back to the Rabbit family.

01:13

If there are 49 children and each has 37 kids of their own,

01:17

we can multiply 49 by 37 to get the number of grandchildren.

01:21

To solve, we’re going to work backwards through 37’s digits… [Man gesturing to cars walking backwards]

01:25

…first multiplying by 7…

01:27

…then multiplying by the 3 in the tens place, which is actually 30.

01:31

So first, we need to find 49 times 7.

01:34

7 times 9 is 63. Write the 3, carry the 6.

01:37

7 times 4 is 28, plus the carried 6 is 34.

01:42

When we write down 34… we get 343.

01:46

Next multiply 3 by 49.

01:49

Repeat the steps we just did, multiplying 3 by 49, but this time write a zero before [Bunny hops up the stairs]

01:54

you begin, since our 3 is actually a 30.

01:56

3 times 49 comes out to 147, so we get 1,470.

02:02

Next add 343 plus 1,470.

02:06

3 plus 0 equals 3.

02:09

4 plus 7 equals 11, so we write 1 and carry the other 1.

02:13

3 plus 4 plus the carried 1 equals 8. And 1 plus nothing equals… 1.

02:19

That means there are 1,813 grandkids…but don’t forget we still have to add the 49 kids. [Jack and Bunny's children and grandchildren]

02:27

Well, we get 1,813 plus 49….3 plus 9 is 12… write the 2, carry the 1… 1 plus 4 plus the carried

02:34

1 gives us 6…and we can drop down the 1 and the 8…

02:38

…to give us 1,862 total kids and grandkids with tummies a-rumblin’.

02:43

We really don’t envy Jack and Bunny.

02:45

Especially at tax time. It must be a nightmare trying to claim that many dependents. [Jack and Bunny in the kitchen with the kids and grandkids]

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