Wednesday, September 25, 2013

Subtraction and Sibling Rivalry

I don't normally post about things like this on here, but this seemed too long for a Facebook status :).

A discovery I've made as a homeschool mom is that a secret to teaching subtraction is....exploiting sibling rivalry. 

Not what you're thinking. No--I don't mean setting your kids up to compete with each other. I mean, use their rivalry to help them understand practical application of math concepts.

For example...

This is the word problem you're given:
Suzie has 14 crayons. Mary has 18 crayons. What is the difference?
You have explained to your child about 4,327 times that "what is the difference" means you subtract. Still, she looks at you like you're speaking another language. So you reword it and ask, "How many more crayons does Mary have than Suzie?" Again, a blank stare.

Now, say this:
You have 14 crayons. Your brother has 18 crayons. What is the difference?
What immediately goes through your child's mind:
He has MORE than me. This is UNACCEPTABLE. 
And the calculation will happen almost instinctively. Actually, she will also be able to tell you that if he gives her two crayons, they will now have THE SAME.

Another example... 
4 - 2 1/3 = ?
What is probably going through both your head and your child's:
Fractions??? Are you kidding me? 
A common problem is getting the fraction on the "wrong side"--in other words, your child may answer "2 2/3" or even "2 1/3" because 4-2=2, and they're not sure what to do with the fraction part.

Never fear. Say this:
You have 4 brownies. I'm going to give your sister 2 1/3. How much will you have left?
Your child will immediate envision four brownies sitting in front of him. He will fully understand that TWO WHOLE BROWNIES will be taken from this precious stash. And not only that, but 1/3 of one of the other will be given to her. Which is, of course, unacceptable. And you may be surprised that he can not only answer the question, but tell you exactly how much his sister needs to give back in order to make them have THE SAME.

Notice--"the same" is of utmost importance.

And of course my disclaimer that I can't guarantee this will work with your kid, but my little Beasties.... ;)


Sonja Hutchinson said...

Sing it, Sister! My two boys are the same way, and this works with them every time. Obviously, they've forgotten all the times I told them "life isn't fair" and that equal shares aren't always a guarantee...

Good strategy, anyway.

Caprice Hokstad said...

This works best when the mythical item (such as brownies) is something the child wants. All too often when I have tried to keep it close to the book example, my kid DOES NOT CARE. "Let my brother have all the freaking carrots. I don't like carrots." Obviously, with food, I can most times guess what will work, but I also had one kid who was so not a foodie that she actively tried to work the math so that she could get rid of this pesky food because IT was obviously a source of headache (i.e. IT made math, so give away the food and my math will go away.)

Sparks of Ember said...

lol - that is very, very true! I have distinct memories of my siblings & I literally counting the Cheezits to make sure we all had the exact same amount. And if there were a few extra left-over, no one ever agreed that I should get them as the oldest - nope, my parents had to take them. ;)

Kat Heckenbach said...

Hah, yes, kids always seem to forget life isn't fair when it comes to what they want :).

And yes, I agree that it works FAR better when you change the object to something specifically of interest to them. I change a LOT of things to video games for Beastie 1 :P.

And my Beasties do that too--counting to make sure they get exactly the same!

Cheryl Johnston said...

Two questions, Kat: 1) Are those brownies homemade? and 2) May I have 2 please?

Loved this post!