There are two barrels, A and B. The A barrel is filled with 1 liter of oil, and the B barrel is empty. Pour the oil in barrel A to barrel B (1/2) for the first time, pour the oil in barrel B to barrel A (1/3) for the second time, and pour the oil in barrel A to barrel B for the third time (1/4), for the fourth time pour the oil in barrel B to barrel A (1/5). So repeated, regardless of consumption, poured 19 times, how many liters of oil are in barrel A?
甲、乙两个桶，甲桶内装了1升油，乙桶是空的．第一次把甲桶的油倒给乙桶(1/2)，第二次把乙桶中的油倒给甲桶(1/3)，第三次把甲桶中的油倒给乙桶(1/4)，第四次把乙桶中的油倒给甲桶(1/5)．如此反复，不计消耗，倒了19次，甲桶中有多少升油．
<gadget id="calculator">3 / 1</gadget>
<output>3</output>

<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">5 / 6</gadget>
<output>5/6 = around 0.833333</output>

<gadget id="calculator">(3/5) * (5/6)</gadget>
<output>1/2 = around 0.5</output>

<result>1/2 = around 0.5</result>