A total of 90 trees were planted in the fourth grade, and the number of trees planted in the fifth grade was 20 times less than that in the fourth grade. How many trees were planted in the fifth grade?
四年级一共栽树90棵，五年级栽的棵数比四年级的2倍少20棵，五年级一共栽树多少棵？
<gadget id="calculator">90 * 2</gadget>
<output>180</output>

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

<result>160</result>