The school planted 50 trees, and the survival rate was 90%. How many trees survived?
学校植树50棵，成活率为90%，成活了多少棵．
<gadget id="calculator">90 / 100</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">50 * (9/10)</gadget>
<output>45</output>

<result>45</result>