Math in the age of iPhones


Worried about ‘numeracy’? Teach your kids to multiply.

There, I’ve said it! I think kids should learn multiplication

I’m good at math. I’m also good at judo. What do those two have in common? I’ve done an extraordinary amount of both. It’s not a radical notion that the more you do of anything, the better you get at it. Only last week, Daniel Mondaca wrote a post about learning a second language improving the brain’s ability to learn new things.

The more kids work with numbers, the better they get at math

Working with numbers can mean a lot of different things. I’m in favor of manipulatives and yes, *gasp*, memorizing multiplication tables but those are posts for another day. Today, I want to argue very strongly that

Two- and three-digit multiplication is worth learning, even if everyone has a calculator app in their pocket.

Let’s take the video below as an example. We multiply 892 x 11.

Honestly, if I need to multiply two- and three-digit numbers. I use my phone.

Our CEO, Maria Burns Ortiz

So, do I, usually, but there is still a lot of value in having students multiply with a pencil and piece of paper or in their heads. Quite a bit of math is explained in this video, as demonstrated below.

Estimation is the most practical math skill

There are a lot of mathematics concepts, that I use regularly writing software or computing statistics in my day job. The one skill I use all the time, everywhere is estimation, and I can tell you that the ability to accurately estimate an answer is not universal.

In the problem in the video above, we round 892 to 900 and can estimate that our answer should be near to – and less than – 9,900.

Let’s say you type the wrong number in your phone, hitting the 6 instead of the 9, since these two are pretty close and you have big fingers. Now your answer is 7,612. If you have a good grasp of estimation and multiplication, that is clearly wrong. If you’re computing how much money you need to charge a customer based on the 892 hours you expect to work at $11 an hour, you have just lost out on over $2,000!

A different example of estimation

…. comes from the second video below. Here, because the last digit of one number is 7 and of the other number is 2, you know that 7 x 2 = 14. So, whatever else your answer is, it has to end in a 4.

Now, if you are a very young person, just learning math, you may ask,

Small child asking about multiplication

“How do you KNOW that?”

Watch the video.

The fact is that the more experience you have with numbers, the more problems you solve, the easier it gets.

Also, all of those basic facts you learn, like 2 x 7 =1 4 are truly the basis for understanding ideas like the commutative property of multiplication or reducing numbers to lowest terms or solving equations by multiplying or dividing both sides by a constant. You need a BASE to work from, problems that can be examples.

Do I mean kids should do 100 worksheets? Yes and No.

I think you can’t just do 7 problems and call it a day. We have now mastered multiplication. Tomorrow, division.

Here is a program to create worksheets of random problems.

I recommend:

  1. Have the students try to solve 3 to 5 problems- 10 minutes
  2. Watch the first video – 3 minutes
  3. Try another 3 to 5 problems – 10 minutes
  4. Watch the second video – 3 minutes
  5. Do another 3 to 5 problems – 10 minutes
  6. Discuss with students if any of the strategies helped them solve the problems, and if so, which ones – 10 minutes

That’s one lesson, one day. They’ve done 9-15 problems working at their own pace. They’ve heard three different strategies for solving multiplication of 2- and 3-digit number problems with two examples of problems. These strategies, of course, can be applied in different types of problems.

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