Sixth grade teachers and students donated 140 books to Hope Primary School, the number of books donated by sixth grade is that of fifth grade (2/7), how many books donated by fifth grade?
六年级师生向希望小学捐书140本，六年级的捐书数是五年级的(2/7)，五年级捐书多少本？
<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">140 / (2/7)</gadget>
<output>490</output>

<result>490</result>