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Course: Class 3>Unit 4

Lesson 1: Intro to multiplication

Multiplication on the number line

Sal uses a number line to represent and solve simple multiplication expressions.

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• why is the answer the same if you do it both ways
7x3=21 and 3x7=21
• This is an important property of multiplication called the commutative property. We can multiply numbers in any order and get the same answer.

Think of 3x7 as the number of (smallest) squares in a grid with 3 rows and 7 columns.

Think of 7x3 as the number of (smallest) squares in a grid with 7 rows and 3 columns.

Turning either one of these two grids 90 degrees gives the other grid. Turning a grid does not change the number of (smallest) squares.

So it makes sense that 3x7 is the same as 7x3.

Have a blessed, wonderful day!
• How do you use multiplication on a number line?
• First, you break the multiplication down, for example: 4*4 is the same as 4+4+4+4. So on a number line, you would start at 0, and "jump" 4 places 4 times. and since there were 4 "jumps" of 4 places, the expression would be 4*4.
• how do i multiply on a numberline to 100
• by drawing out the numberline from 0 to 100

As you would notice though it would end up too long. There's techniques used to deal with big multiplication like 100 by using patterns found in multiplying by 10s and 1s

For example, if you draw a number line of any number and skip count to 10 you'll notice they'll all end up with an extra 0

Say like 2

10 + 10 = 20

lets try 5

10 + 10 + 10 + 10 + 10 = 50

See the trend of how anything multiple by 10 is just the number with a zero?

Now what would happen if I added an extra zero(100)?

And that's how you would address your number line issue.. by not using a number line
• At about minutes into the video Sal says; 'seven equal hops'. What does he mean by this?
Why did he mention the word 'equal'?
They've got to be equal hops / groups right?
• "7 equal hops" means that he is moving forward 7 times, each time moving the same amount on the number line.
• Why do we skip count
• could you times inf
• yes you can but you will get the same number
(1 vote)
• because it is a flip flop
• i need help with the one plus 55555555555.5 and the square root of 98
(1 vote)
• 55555555555.5 + 1 = 55555555556.5 I think
the square root of 98 is approximately 9.9 (9.89949494) lol
• 9 times table is easy with two patterns
(1 vote)
• When we multiply 9 by a whole number from 1 to 10, the tens digit of the answer is one less than this whole number, and the units digit of the answer is 9 minus its tens digit.

Example: 9 x 7
The tens digit is 7-1 = 6.
The units digit is 9-6 = 3.