Back from my mini-Spring Break getaway and eager to get back to work on my newest product, which features adorable monkeys and focuses on addition, subtraction, and place value. Which brings up the question, how many ways can you add 34 and 28? Like many of you, I was taught the traditional algorithm for adding multi-digit numbers. And when I learned it, there was not even any mention of place value–8 + 4 = 12, write down the 2 and carry the 1. Sadly, there are still teachers today who teach the algorithms for addition and subtraction in a completely rote manner.
So here’s a few different ways you might add these two numbers (adapted from Van de Walle, Teaching Student Centered Mathematics, K-3).
- Use multiples of 10: I know that 20 more than 34 is 54 (give kids lots of practice doing this on a 100 chart). Six more gets me to 60, plus 2 more is 62 (notice that I broke apart the 8 into 6 and 2).
- Add the tens and then the ones: 20 + 30 = 50 and 4 + 8 = 12 (I would probably think of this as 8 + 2 to make a 10 and then 2 more). 50 + 12 = 62.
- Move some to make 10s: I can move 2 from the 34 (leaving 32) to the 28 to make 30. 30 + 32 = 62.
- Use friendly numbers and adjust: 28 is pretty close to 30. 30 and 34 is 64, but I have to take off 2, because 30 is 2 more than 28, so it’s 62.
For more on addition, number sense, and place value check out Monkey Business, Adding Tens and Place Value Workstation Activities.