The number of students in the third grade is 75% of that in the fourth grade, and there are 120 students in the third grade. How many people are there in the third and fourth grades?
三年级人数是四年级的75%，三年级有120人．三、四年级一共有多少人？
<gadget id="calculator">75 / 100</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">120 / (3/4)</gadget>
<output>160</output>

<gadget id="calculator">160 + 120</gadget>
<output>280</output>

<result>280</result>