Thinking about Subtraction

Dear Grade 3's & Parents,

Today we learned a different way to subtract. It challenged you to be more thoughtful about your understanding of place value.  Here is an example of what you learned today:

          384 "Minuend"
       -  245 "Subtrahend"
______________________

ones  -------- 4 - 5 = ?
tens   -------- 80 - 40 = ?
hundreds --- 300 - 200 = ?

The problem is the ones/units place (4 subtract 5) does not work, as we know a smaller number cannot subtract a larger one.  So, to regroup I need to take "10" from the tens place, making the problem:

ones ------ 14 - 5 = 9 (notice by regrouping, that 4 has become 14)
tens  ------ 70 - 40 = 30 (notice by regrouping, that 80 has become 70)
hundreds ---- 300 - 200 = 100 (nothing changes here as the numbers work together)

I can now solve the whole problem by adding up all my differences 100 + 30 + 9 = 139.

The answer is 139, which is the "difference."

Now to check the answer, you would add up your difference and subtrahend to get the minuend:
139 + 245 = 384.

I know this looks slightly different than on the Smartboard and your math notebooks. Try a practice question at home with you parents tonight. If you continue to find this new way of subtracting challenging, don't worry as we will work on this again tomorrow.

Remember to read tonight.

See you tomorrow.

Ms. Toy