Because only one number is needed, there is no need to consider the number of other numbers, and other numbers are also very special.

Whether it is addition, subtraction, multiplication and division (without division), what he works out is a few, and nothing will change because of carry or reduction.

For example, the single digit of 23 15234+2345345 is 9, unlike other digits, we should consider what the last digit is.

For example, the unit number of 23 15234*2345345 is 0. It is easy to know this rule.

Let's take a number, 8 to the power of 1998.

First, let's look at the law of 8 to the nth power.

1 power of 8

The secondary bit of 8 8*8=64 is 4.

The cube of 8 4 * 8 = 32 is 2.

The fourth power of 8 2 * 8 =16 is 6.

8 to the fifth power 6*8=48 is 8.

8 to the sixth power 8*8=64 is 4.

8 to the seventh power 4*8=32 is 2.

Take a closer look. It doesn't need four consecutive powers as a cycle.

1998/4=499 Yu 2

In other words, the unit of 8 to the power of 1996 is 6, so his unit of 1998 is 4!

Others and so on.