The number of red goldfish in the fish tank is three times that of black goldfish. If the total number of goldfish in the fish tank is reduced by 10 and the number of black goldfish is increased by 5, the ratio of the number of red goldfish to the number of black goldfish will become 2:1. Find the fish tank How many goldfish are there in the original.
鱼缸里红金鱼数是黑金鱼的3倍，如果把鱼缸里的金鱼总数减少10条，黑金鱼的数增加5条，那么红金鱼数与黑金鱼数之比会变成2：1，求鱼缸里原来有多少条金鱼．
<gadget id="calculator">2 * 5</gadget>
<output>10</output>

<gadget id="calculator">10 + 5 + 10</gadget>
<output>25</output>

<gadget id="calculator">3 - 2</gadget>
<output>1</output>

<gadget id="calculator">25 / 1</gadget>
<output>25</output>

<gadget id="calculator">25 * 3</gadget>
<output>75</output>

<gadget id="calculator">75 + 25</gadget>
<output>100</output>

<result>100</result>