Three Is a Magic Number: School House Rock video about multiplying by Three.

Lyrics

It takes three legs to make a tripod or to make a table stand
It takes three wheels to make a vehicle called a tricycle
Every triangle has three corners
Every triangle has three sides
No more, no less
You don't have to guess
When it's three you can see it's a magic number

A man and a woman had a little baby
Yes, they did
They had three in the family
And that's a magic number

Now, the multiples of three
Come up three times in each set of ten
In the first ten you get 3, 6, 9
And in the "-teens" ten it's 12, 15, and 18
And in the "twenties" you get 21, 24, 27
And it comes out even on 30

Now multiply backwards from three times ten

3 x 10 is 30
3 x 9 is 27
3 x 8 is 24
3 x 7 is 21
3 x 6 is 18
3 x 5 is 15
3 x 4 is 12
And 3 x 3 is 9
And 3 x 2 is 6
And 3 x 1 is 3 of course

3 x 10 is 30 (keep goin')
3 x 9 is 27
3 x 8 is 24
3 x 7 is 21
3 x 6 is 18
3 x 5 is 15
3 x 4 is 12
And 3 x 3 is 9
And 3 x 2 is 6
And 3 x 1... What is it?
Three!
Yeah...
That's a magic number

A man and a woman had a little baby
Yes, they did
They had three in the family
That's a magic number