## Thursday, April 2, 2015

### Lining Up the Decimals... It Just Doesn't Add Up

My daughter and I have been talking a lot about math. Maybe that is because I love math, maybe it is because we home school, maybe it is because math is applicable to so many topics.... Whatever the reason may be, we have found our way to decimals.

We have begun talking about the tenths and hundredths place, we have  looked at how these decimals would appear as fractions, compared and ordered. So when I found my daughter counting up the change in her piggy bank, I figured this was the perfect time to introduce some adding.

We have a huge chalk board. I wrote the problem 0.34 + 0.15 and asked her to add. She quickly got 0.49, but it wasn't so easy for her to explain to me how she got it. She gave me the typical student response, "I just added." So then I wrote the problem 0.7 + 0.24 on the board and asked her to use any method she wanted to add them together. Again, she quickly added them together and got..... 0.31!

Seeing her answer and knowing what she had done, I found this to be a great time to go back to that piggy bank. We broke down the problem like this:

0.7           +           0.24
7 tenths      +      2 tenths + 4 hundredths
7 dimes      +      2 dimes + 4 pennies

Why did we do this? Well, just simply telling students to "line up the decimal points" doesn't work because they don't understand why they are lining them up and sometimes, they don't even understand what that really means. Trust me, I saw it year after year in middle school and I even see it now with my adult students.

So first we broke it up by place value. And this might have been enough to get the point across. Now my daughter could see we have 9 tenths and 4 hundredths or 94 hundredths or 0.94 or 94/100 or 47/50.... (We like practicing writing numbers in different forms!!)
I took it another step to bring it back to the money so that she had something she could picture in her mind to help it make even more sense. Once we were done discussing, she was able to write the problem correctly, lining up the place values. But she didn't do this because I simply told her to; she did it because it now made sense. She even intuitively filled in a zero after the seven to make it 0.70 + 0.24. Time will tell if she will continue to remember how to add decimals together, but I think we are off to a good start.

Next up, throwing in some whole numbers (dollars) to see if she can figure out where they will go in the whole adding process and of course, some subtraction!

What math are you doing these days? Does math naturally appear in your every day?