## Wednesday, May 31, 2006

### Finger Arithmetic Part One of Many

Continuing finger arithmetic from part zero. The second part is called part one. Just as the century with the years numbered mostly in the 1900's is called the twentieth century. What a nuisance. But thinking about these issues can prepare one to be capable of dealing with all sorts of off by one errors, such as fence post errors. And, zero is the most important number. Nothing is more important than all of mathematics. Nothing.

Each hand is one digit of a two digit number.

Your right hand is the one's digit. It can count from zero to nine. Your left hand is the ten's digit. It can count from zero to ninety, by tens. This isn't a left handed or right handed thing. It's just that when you look at Arabic numbers, the least significant digit is on the right.

Make a fist with both hands. That's zero (00). Say it.

Put up a finger on your left hand. Say 'ten'. Say it out loud.

Add another finger on your left hand. Say 'twenty'. Don't by shy.

Add another finger on your left hand. Say 'thirty'. I can't hear you.

Add another finger on your left hand. Say 'forty'. Shout if you must.

Make a fist with your left hand and stick out the thumb. Say 'fifty'. That's right. Your left thumb, all by itself, is the most valuable.

Add a finger to your left hand. Say 'sixty'. It is just as important to learn to read your hands as it is to get the movements right.

Now we'll represent some two digit numbers.

Set twenty nine. Start with zero - two fists. Stick out two fingers on the left hand. Stick out your right thumb and all four fingers. Say 'twenty nine'.

Add one. Since you have twenty nine you have to make a fist with the right hand and add a finger to the left hand. Say 'thirty'.

Set forty nine. Start with zero - two fists. Stick out four fingers on the left hand. Stick out your right thumb and all four fingers. Say 'forty nine'.

Add one. Since you have forty nine, you have to make a fist with the right hand, and add one to the left. Since you don't have one to add, make a fist and stick out your thumb. Say 'fifty'.

Now count from zero to nineteen. That's right, you start by counting from zero to nine on your right hand. Then you make a fist with the right hand and add one finger on your left hand, to get ten (10). With the left hand showing one finger, count to nine with your right hand. That's ten to nineteen. You were counting out loud, right?

More exercises. Count from zero to twenty. Count from forty to sixty. Count backwards from sixty to forty. You were counting out loud, right?

Extra credit: count by tens backwards from ninety to zero.

That's two digit counting. Remember to practice the drills every day. Don't forget to bring your fingers with you, everywhere. Do you have five minutes? What are you waiting for?

Another hint. If you have something to put your fingers on, like a table, or your knee, you can have a finger or thumb be active when it is touching. That way you don't have to look. Tactile feedback is a good thing. But remember not to get lazy and rest your hand - it messes up the current number.

An aside. I can count from zero to one thousand twenty three on my ten fingers. I don't find it handy. There are ten kinds of people in the world. Those that understand binary, and those that don't.