The school planted 500 trees in spring last year, with a survival rate of 85%. The survival rate of tree planting in autumn last year was 90%. It is known that 20 more trees died last spring than in autumn. How many trees did the school plant last year?
学校去年春季植树500棵，成活率为85%，去年秋季植树的成活率为90%，已知去年春季比秋季多死了20棵树，去年学校一共种活了多少棵树？
<gadget id="calculator">85 / 100</gadget>
<output>17/20 = around 0.85</output>

<gadget id="calculator">500 * (17/20)</gadget>
<output>425</output>

<gadget id="calculator">1 - (17/20)</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">500 * (3/20)</gadget>
<output>75</output>

<gadget id="calculator">75 - 20</gadget>
<output>55</output>

<gadget id="calculator">90 / 100</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">1 - (9/10)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">55 / (1/10)</gadget>
<output>550</output>

<gadget id="calculator">550 * (9/10)</gadget>
<output>495</output>

<gadget id="calculator">425 + 495</gadget>
<output>920</output>

<result>920</result>