Another way to do subtraction

No more borrowing and paying back, or the new alternative

Use addition and then simple subtraction, naturally there are several steps

Example     234 – 187

234

-187  (should be lined up!)

Now 7 is greater than 4,  so we add 3 to both numbers, giving a zero in the units position of the second number

234 -187 = 237 – 190   (must be able to add 3 to 187 !!!)

moving to the 10’s position, and very formally, 90 is greater than 37 so add 10 to both numbers, giving

237 – 187 = 247 – 200, which is now simple, with result  47

Of course, if the lower digit is less than the one above just subtract it from each number

234 – 117 = 237 – 120 = 214 – 100 = 114

It is best to keep the “one above the other” layout, but I have fought with the editor enough today.

Advertisements

1 Comment

Filed under arithmetic

One response to “Another way to do subtraction

  1. I am following you now. This is a version of equivalence statements or sentences, something I was going to blog about later this summer. Equivalence statements are a great way to expand student’s thinking and get them to formulate faster mental calculations. Thanks for the post!

My wordpress emails suddenly disappeared last night ??????

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s