Last night, Dad asked Doudou to pour him a glass of water. Doudou picked up the water glass and found that there was already some water in the glass. She doubled the water and put it on the electronic scale. The number displayed on the display was 1.5 kg, she added 4 times the original amount of water, the number displayed on the screen was 2.5 kg, how many kg of water was in the cup?
昨天晚上，爸爸让豆豆给他倒杯水，豆豆拿起水杯，发现水杯内已有一部分水，她把水加到原来的2倍，放到电子秤上，显示屏上显示的数子是1.5千克，她把水加到原来的4倍，显示屏上显示的数子是2.5千克，杯子里原来有水多少千克？
<gadget id="calculator">2.5 - 1.5</gadget>
<output>1</output>

<gadget id="calculator">4 - 2</gadget>
<output>2</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

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