This year's Arbor Day, the students planted 180 trees, 20 of which did not survive. Later, we replanted 20 trees and all of them survived. What is the survival rate of the students planting trees this year?
今年植树节，同学们种植了180棵树，有20棵没有成活，后来大家补种了20棵，全部成活．今年同学们植树的成活率是多少．
<gadget id="calculator">180 - 20</gadget>
<output>160</output>

<gadget id="calculator">160 + 20</gadget>
<output>180</output>

<gadget id="calculator">180 + 20</gadget>
<output>200</output>

<gadget id="calculator">180 / 200</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">100 / 100</gadget>
<output>1</output>

<gadget id="calculator">(9/10) * 1</gadget>
<output>9/10 = around 0.9</output>

<result>9/10 = around 0.9</result>