More often than not, more is less

In the summer, Costco peddles a buttload of educational workbooks. You know the ones: collections of every worksheet necessary for your child to complete <insert grade here> Math. Can’t find them? Look over by the Christmas trees.

I picked up the Grade 3 book. Just browsing. Killing time. I opened to this page:

add:subtract words

I’m not a big fan of this approach. Forget about comprehension, just scan for the add or subtract words. See more, think add. But it’s not that easy. More shows up in five of the practice exercises. Try them.

  • In the picture, how many more 4-legged animals are there than 2-legged ones?
  • Peter has 39 goats.  He wants to have 64 goats.  How many more goats should he buy?
  • Peter has 68 animals on his farm.  He buys 23 more.  How many animals does he have now?
  • 413 gulls are joined by 311 more.  Then 136 more gulls come.  How many gulls are there altogether?
  • There are 576 gulls, but 153 fly away.  Then 283 more leave.  How many gulls remain?

A mountie (really?!) tells kids (Canadian, no doot) to decide on the operation.

mountie

From the answer key:

  • In the picture, how many more 4-legged animals are there than 2-legged ones? 15 − 12 = 3
  • Peter has 39 goats.  He wants to have 64 goats.  How many more goats should he buy? 64 − 39 = 25
  • Peter has 68 animals on his farm.  He buys 23 more.  How many animals does he have now? 68 + 23 = 91
  • 413 gulls are joined by 311 more.  Then 136 more gulls come.  How many gulls are there altogether? 413 + 311 + 136 = 860
  • There are 576 gulls, but 153 fly away.  Then 283 more leave.  How many gulls remain? 576 − 153 − 283 = 140

Subtraction is used to answer three of five questions with this ‘add’ word. Actually, kids will think addition for the first two questions (12 + 3 = 15 and 39 + 25 = 64) but that’s another post.

Teaching Improper Decimals Using Ten-Frames

Professor Triangleman posed an interesting question a few weeks back:

If 15/10 is an improper fraction, then shouldn’t 1.5 be an improper decimal? Or is 1.5 a mixed decimal, having more in common with the mixed fraction 1 5/10? Both? Neither?

One definition of decimal:

A fraction whose denominator is a power of ten and whose numerator is expressed by figures placed to the right of a decimal point.

Thus, in 1.5, the implied denominator is 10 and the implied numerator is 5, the figure to the right of the decimal point. We read 1.5 as “one and five tenths,” a mixed decimal. The whole number part is treated separately, making an improper decimal an impossibility.

But what if we didn’t just look at the figures to the right? Nested tenths don’t stop/start at the decimal point. What if we looked at all the figures? We’d read 1.5 as “fifteen tenths,” an improper decimal.

Maybe the improper vs. mixed comparison is throwing me off track. Fractions can be classified as either proper or improper. Why not decimals? Decimals less than one, such as 0.5, would be proper; decimals greater than or equal to one, such as 1.5, would be improper (or, in Britain, top-heavy).

Christopher Danielson wasn’t trying to introduce new vocabulary to the world of math(s). Probably. Rather, he was making a point about place-value.

When we teach decimals using ten-frames we do.

If the whole is one full ten-frame, students may build 3.7 like this:

37

Students will describe 3.7 as “3 ones and 7 tenths,” “37 tenths,” or even “2 wholes and 17 tenths.” This mirrors what students know about place value and whole numbers: 37 can be described as “3 tens and 7 ones,” “37 ones,” or even “2 tens and 17 ones.”

Just like with whole numbers, thinking about place value makes calculations with decimals easier. For example, consider 4.8 + 3.6:

48 plus 3650 plus 34

  • 4 and 3 make 7
  • 0.8 (“8 tenths”) and 0.6 (“6 tenths”) make 1.4 (“14 tenths”)
  • 7 and 1.4 (“1 and 4 tenths”) make 8.4 (“8 and 4 tenths”)

Note the shift in thinking, not notation, from 1.4 as “14 tenths” to 1.4 as “1 and 4 tenths.” With fractions, it’s a shift in thinking and notation. Probably why we know about improper fractions but not improper decimals.

Blackline Masters:

Ten-Frames – Full
Ten-Frames – Less-Than-Ten
Ten-Frames – Place Value Mat

Math Picture Book Post #1: Cats’ Night Out

My background is in secondary, but I have spent the majority of the past two years in elementary. This blog hasn’t always reflected that shift. This year, I plan to blog more about my experiences teaching math in K-7.

Often, I use picture books to launch math lessons. Picture books allow teachers to leverage literature-based methodologies. The plan is to make this a series of posts.

I classify math picture books into three categories:

  1. mathematics is explained
  2. mathematics is weaved into the storyline
  3. mathematics is hidden

Books in the first category are, by and large, horrible. The reader is told that learning a particular mathematical concept is important and this concept is explained. Sometimes, art imitates life and a teacher-like character explains a topic to student-like characters. That’s just cheating.

There are some great picture books in the second category. In these books, math (not the characters’ learning about math) is central to the story. For example, in Bean Thirteen by Matthew McElligott, divisibility is introduced when the characters don’t want to get stuck with the unlucky thirteenth bean. In If a Chicken Stayed for Supper by Carrie Weston, part-part-whole relationships are explored when each fox counts the others and concludes someone is missing. Often, these books provide more questions than answers.

Books in the third category are the most difficult (and most rewarding– think #anyqs) to find. In these books, the author did not set out to write a math book. You won’t find these books in the math section of your local independent bookstore. But the math is there if the reader looks at the story through a mathematical lens. (More on this later.)

This week’s math picture book is Cats’ Night Out by Caroline Stutson. I’d place it in the second category. It’s a counting book and that might stretch your idea of ‘storyline’. (That’s fine.) Counting by twos from two to twenty, each page is illustrated with cats dancing in the city. Here are the pages for eighteen:

How did you see 18? I first saw 9 on each page (5 and 3 and 1). Students could draw their own pictures of doubles on folded paper. Also, on the two pages there are 9 white cats and 9 black cats. Kids will find two 9s in other places. There are 9 cats with bows and 9 cats without. Doubles can also be seen in rows across the pages. For example, double 5 can be seen across the bottom row. The use of doubles is a strategy for mastering addition (and multiplication) facts.

These 10 cats can be seen in another way. There are 6 white cats and 4 black cats across the bottom row. Students could be asked to find ways of making a different number of cats or different pages could be copied and students could look for different part-part-whole relationships. This, too, helps students master addition facts. For example, 9 + 3 can be thought of as 9 and 1 makes 10 and 2 more is 12; 6 + 7 can be thought of as double 6 makes 12 and 1 more is 13.

My love of card stock and the laminator has been well-documented. For teachers wanting to use pictures of these cats, here you go: Cats’ Night Out Cats (Large) & Cats’ Night Out Cats (Medium)

Two-Digit Addition – When Do I Show Them the “Real” Way?

Last week, I attended Carole Fullerton‘s parent presentation. She discussed strategies students have for adding two-digit numbers. Carole’s timing was great since I’ve been having similar discussions with teachers in recent weeks.

How many ways can you add 59 + 37?

The most common strategy that I see students use is to add the tens, add the ones, and then combine. Students working with ten frames naturally begin by grouping the 10’s, not the 1’s, together.

Students find other strategies. For example,

  • Add 1 to 59 to make 60. Take 1 away from 37 to make 36. 60 and 36 is 96. (make ten)
  • Add 1 to 59 to make 60. Add 3 to 37 to make 40. 60 and 40 is 100. Take the extra 4 away. (friendly numbers and compensation)
  • 30 more than 59 is 89. 7 more than 89 is 96. (add on)

These are the strategies I use to compute mentally. On paper, I fall back to the traditional right-to-left digit algorithm. It’s the result of performing thousands of such calculations in elementary school.

Students should be encouraged to write their mental math strategies down on paper. Some students will have to.

Teachers and parents appreciate these strategies. They make sense. Teachers and parents want mathematics to make sense to their kids. But at some point they always ask the question: “When should they learn the traditional/regular/real way?” They ask this because they are concerned their kids will not be prepared. “But do these strategies work for three-digit addition?” Yes.

“Relax. This will look familiar,” Carole joked. The same natural left-to-right strategy described above can be written vertically. We start with 50 and 30 is 80. Already, we know the sum is greater than 80.

Compare that with the traditional algorithm. We start with 9 and 7 is 16. We know the sum will have a 6 in the one’s place.

Which piece of information is more important? Carole made the point that accuracy is important. Always was, always will be. But it’s not where we should start. Strategies should be built on conceptual understanding. The emphasis of a left-to-right strategy is on number whereas the emphasis of a right-to-left strategy is on digits.

In her new blog, Amy Newman also writes about this. As well, she shares Carole’s key messages for parents helping children at home.