Assume that the amount of resources newly generated by the earth each year is constant. According to calculations, all the resources on the earth can be exhausted for 11 billion people to live for 90 years, or for 9.9 billion people to live for 210 years. How much must the world's total population be controlled in order to ensure that the resources on the earth are sufficient to allow human beings to continue to reproduce? Use equations and formulas in two ways.
假设地球每年新生成的资源的量是一定的．据测算，地球上的全部资源可供110亿人口生活90年而耗尽，或者可供99亿人生活210年而耗尽．世界总人口必须控制在多少以内，才能保证地球上的资漉足以使人类不断繁衍下去？用方程和算式两种方法．
<gadget id="calculator">99 * 210</gadget>
<output>20_790</output>

<gadget id="calculator">110 * 90</gadget>
<output>9_900</output>

<gadget id="calculator">20_790 - 9_900</gadget>
<output>10_890</output>

<gadget id="calculator">210 - 90</gadget>
<output>120</output>

<gadget id="calculator">10_890 / 120 / 1</gadget>
<output>363/4 = around 90.75</output>

<result>363/4 = around 90.75</result>