Subtraction!

We started this week learning about two digit subtraction.  It quickly got tricky as we learned that sometimes we need to "borrow" when there are not enough ones.  When subtracting from a two digit number, follow the steps below:

1) Check to see if you need to borrow. If yes, go to step #2.  If no, go to step #4.
2) Cross out the number in the tens place.  Write the number one less above it.
3) Cross out the number in the ones place.  Write the number ten more above it.  (This is instead of squeezing in a little 1 like we were probably taught)
4) Start in the ones place - subtract.
5) Move to the tens place - subtract.
6) Check your work!  Ask your child how s/he can check the answer to a subtraction problem. (By adding the answer - the difference - to the bottom number of the equation.  That will total the number you were subtracting from.)


Example:

    4  12
    5   2
  - 2   8
     2  4

Think:  I can't subtract 8 from 2, so I need to borrow a 10.  Cross off the 5.  Instead of 5 tens, I now have 4 tens.  Cross off the 2.  Instead of only 2 ones, I now have 12 ones.  (4 tens and 12 ones is the same as 5 tens and 2 ones)  Then I subtract:  12 - 8 = 4.  4 - 2 = 2.
Check!  4+8=12.  2+2=4.  
Done!

Check out papers coming home this week that better illustrate the process.  Don't get tricked! Not all subtraction problems require borrowing.  Also, coming soon are papers with mixed addition and subtraction (with and without regrouping, with and without borrowing).