Two-Digit Mental Subtraction

When subtracting two-digit numbers mentally, our aim is to simplify the problem. Let’s begin with this simple subtraction problem :

          87
        -24     (20 + 4)
      ____

Our first step is to subtract 20 from 87 (87 – 20 = 67). Then we subtract 4 to reach the simpler subtraction problem 67 – 4 for our final answer of 63.

The above example is easy because there is no borrowing involve. If a two digit subtraction problem would required borrowing, then round the second number up to a multiple of ten. Subtract the rounded number, then add back the difference. For example :

          84
        -29     (30 – 1)
     _____

So our steps are round 29 to 30, compute 84 – 30 (which is equal to 54), then add back 1 to get 55 as your final answer.

With just a little bit of practice, you will become comfortable working subtraction problems mentally🙂 .

[Home]

Posted on August 15, 2009, in Info Matematik. Bookmark the permalink. 3 Comments.

  1. Cool site, love the info. I do a lot of research online on a daily basis and for the most part, people lack substance but, I just wanted to make a quick comment to say I’m glad I found your blog. Thanks,🙂

    A definite great read.. <a href="http://wiki.hudson-ci.org/display/~bill-bartmann&quot;

    -Bill-Bartmann

  2. Hey, I found your blog in a new directory of blogs. I dont know how your blog came up, must have been a typo, anyway cool blog, I bookmarked you. 🙂

  3. I am always looking for brandnew infos in the WWW about this subject. Thankz.

Leave a Reply

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

%d bloggers like this: