There is a flock of sheep grazing on the hillside. Among them, the white sheep accounted for 45%. At this time, after 16 black sheep came, the white sheep only accounted for 25%. Ask: How many white sheep are there in this group of sheep?
有一群羊正在山坡吃草．其中白羊占45%，这时又来16只黑羊后，白羊就只占25%，问：这群羊中白羊有多少只？
<gadget id="calculator">4 / 0.2</gadget>
<output>20</output>

<gadget id="calculator">45 / 100</gadget>
<output>9/20 = around 0.45</output>

<gadget id="calculator">20 * (9/20)</gadget>
<output>9</output>

<result>9</result>