After the first time, both barrels are 1/2.

After that, barrel B poured into barrel A for the nth time 1/(n+ 1).

Then barrel A pours 1/(n+2) into barrel B.

The available oil quantity of armored barrel is [1/2+1/(n+1)] [1-1(n+2)] =/kloc-0.

That is, it is reversed twice at a time and returns to 1/2.

So the odd number of times is 1/2.

25400 meters

Let a speed be x and b speed be y.

1200- 10x= 10y

100 x- 1200 = 100y

X=66，y=54。

And the value of 100y is the expected value.