**Continuing finger arithmetic from Part Six.**This one is called

*Part Seven*. It is the eighth part in the series.

**Ten's Compliments.**Back in Part Six, we added 7 + 8. We set 7, and added 8 by adding 3 then 5. Adding 3 involved a carry, generating an addition of 5 while remembering that we still have to add 5. Very complicated. This

**Ten's Compliments**idea reduces the steps, and having to remember upcoming steps. It is similar to

**Five's Complements**, introduced in Part Three.

The

**Ten's Compliment**of a number is the number you add to get ten. For now, we'll only use the

**Ten's Compliment**of numbers greater than five. So, the

**Ten's Compliment**of six is four. The

**Ten's Compliment**of seven is three. The

**Ten's Compliment**of eight is two. And the

**Ten's Compliment**of nine is one.

So how does this help? Let's return to the dreaded seven plus eight example. Start with two fists, then set two right hand fingers and the thumb. You'd like to add eight, which is five plus three, but you don't have three to add. Eight is ten minus two (the

**Ten's Compliment**of eight is two). Subtract the

**Ten's Complement**, which is done by subtracting both right fingers. Then add ten by adding a finger to the left hand. Read the result: fifteen. That's ten (the left finger), plus five (the right thumb) and zero (the right fingers). Again, we added 7 + 8, which is 7 - 2 + 10.

How about six plus seven from the last lesson? You do this the same way it was done in the previous lesson. When you have six set, you don't have three fingers to subtract, and you do have two fingers to add. The way it works is that you always have exactly one of these options.

The relevant examples are 6 + 9, 7 + 9, 8 + 9, 9 + 9, 7 + 8, 8 + 8, 9 + 8, 8 + 7, 9 + 7, 9 + 6.

Again, you are referred to the example generator, which can provide you with an infinite number of examples. Each time you click here, you get a new page. Use your back button to get back to the lesson. This is the same link as in the previous lesson.

Technically, we really introduced the

**Ten's Compliment**of five, which is five in Part Five. It wasn't called that, and it just seems simpler to treat it as a special case.

Stay tuned for the introduction of two digit addition.