The school planted 900 trees this year, and the number of trees planted last year was 30% of this year's. How many trees were planted last year?
学校今年植树900棵，去年植的树是今年的30%，去年植树多少棵？
<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">900 * (3/10)</gadget>
<output>270</output>

<result>270</result>