CMUL2

Arithmetic Grade Four

Lesson Forty-six: Column Multiplication

Inspect this multiplication problem:


     15
    x 7 
   -----

There is an extra step that we have to do to get the answer to this problem. We know that 5 x 7 = 35 and 1 x 7 = 7, but how do these two facts help us to get the answer. Here's the problem with the answer:

Here's a step-by-step breakdown of what we have to do:

	STEP ONE: Multiply numbers in ones column. ( 5 x 7 = 35 )
	STEP TWO: Write the 5 under the ones column in the answer row and carry the 3.
	STEP THREE: Multiply the top number in the tens column and the bottom number. ( 1 x 7 = 7 )
	STEP FOUR: Add the 7 from the last step and the 3 which we carried in step two ( 7 + 3 = 10 ) and write the answer starting in the hundreds column in the answer row.

Here are a few more examples for you to study:


	 77			  12 			  21
	x 3			 x 9			 x 8
       -----			-----			-----
	231			 108			 168

Now you will try a few of these yourself.

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