The third grade planted 150 saplings, the fourth grade planted twice as much as the third grade, and the fifth grade planted 50 fewer saplings than the third and fourth grades. How many saplings were planted in the fifth grade?
三年级种树苗150棵，四年级种的是三年级的2倍，五年级种的比三、四年级的总数少50棵，五年级种多少棵？
<gadget id="calculator">150 * 2</gadget>
<output>300</output>

<gadget id="calculator">150 - 50</gadget>
<output>100</output>

<gadget id="calculator">300 + 100</gadget>
<output>400</output>

<result>400</result>