A certain cattle farm raised 690 cattle this year, 15% more than last year. How many cattle were raised last year?
某养牛场今年养牛690头，比去年多15%，去年养牛多少头？
<gadget id="calculator">15 / 100</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">1 + (3/20)</gadget>
<output>23/20 = around 1.15</output>

<gadget id="calculator">690 / (23/20)</gadget>
<output>600</output>

<result>600</result>