There are 840 students in a certain elementary school, the number of students in the first grade accounts for (2/7) of the total number of students in the school, and the number of boys in the first grade accounts for (5/8) of the total number of students in the whole grade. How many boys are there in the first grade?
某小学有学生840人，一年级人数占全校学生人数的(2/7)，一年级男生占全年级人数的(5/8)，一年级男生有多少人？
<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">5 / 8</gadget>
<output>5/8 = around 0.625</output>

<gadget id="calculator">840 * (2/7) * (5/8)</gadget>
<output>150</output>

<result>150</result>