On Mother's Day, (1/3) students in class 51 helped their mothers with housework, (2/5) students said words of gratitude to their mothers, and the rest of the students gave their mothers homemade greeting cards. What percentage of the class is sending greeting cards?
母亲节，五1班有(1/3)同学帮妈妈做家务事，(2/5)同学对妈妈说了感恩的话，其余同学送给妈妈自制的贺卡．送贺卡的占全班的几分之几？
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (1/3) - (2/5)</gadget>
<output>4/15 = around 0.266667</output>

<result>4/15 = around 0.266667</result>