Xiao Ming and Xiao Liang like to collect stamps. The number of stamps for Xiao Ming is equal to (1/5) of the total number of them. If Xiao Ming buys 30 more stamps, his number of stamps is equal to (2/5) of the total number of them. How many stamps did Xiao Ming originally have?
小明和小亮爱好集邮，小明的邮票数等于两人总数的(1/5)，如果小明再买来30张，他的邮票数就等于两人总数的(2/5)．小明原来有多少张邮票？
<gadget id="calculator">5 - 2</gadget>
<output>3</output>

<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">5 - 1</gadget>
<output>4</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(2/3) - (1/4)</gadget>
<output>5/12 = around 0.416667</output>

<gadget id="calculator">30 / (5/12)</gadget>
<output>72</output>

<gadget id="calculator">72 * (1/4)</gadget>
<output>18</output>

<result>18</result>