Subtraction: "Take Away" or "Take It Away!!!"

During a recent conversation with our students, I shared a few secrets.  At the beginning of the year, when we learning how to solve "complicated problems" (multi-step word problems), I told them that when I was in school, I thought math was OK, but it was never my favorite subject (though now I appreciate and understand math much more and *enjoy* the challenge of solving *elementary* math problems).  I also confessed that as a second and third grader, subtraction with regrouping was confusing and difficult for me, especially having to regroup numbers with zeros.  To this day, as an adult, when I need to subtract numbers quickly (Let's be honest...First, I look everywhere around me for things to write with or a calculator!), I often count up from the lower number to find the difference.  Say what?!

Most students are familiar with removal subtraction (take away) situations,

but struggle with comparison subtraction (How many more?  How many less?  Find the difference...).  Over the next couple weeks, we will focus on comparison subtraction problems during Math Workshop.  We will use both "counting up" and "subtracting back" strategies to compare numbers, or tell how far apart they are (their distance from each other/difference).

 Since last month, I have been sneaking these strategies into Calendar Math when we compare the number of days we've been in school to other numbers (How many days since day 9?  How many days until day 50?  100?):

and into an activity we did comparing football scores last week:

and then into other elements of Calendar Math such as when we look at the pictograph we've been making of the weather this month in Jacksonville, FL and Jacksonville, IL: How many more sunny days than partly cloudy days?  Even today, I was talking about how we're approaching the end of the month and will be taking our October Calendar Math assessment and picking new leaders soon: Today is October 23.  How many more days until our test on the 31st?  Comparison problems are everywhere!

Using both of these strategies together also nicely ties in how addition and subtraction are related (they are inverse, or opposite), as we're starting to see while practicing our basic fact families.