Grandma Wang's living expenses for three days are 50 yuan. Among them, (2/5) is spent on the first day, (1/3) is used on the second day, and the rest is the third day's cost. What percentage is the third day's cost?
王奶奶三天的生活费是50元．其中第一天用去的费用占(2/5)，第二天用去的费用占(1/3)，剩下的是第三天的费用，第三天的费用占几分之几？
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 - (2/5) - (1/3)</gadget>
<output>4/15 = around 0.266667</output>

<result>4/15 = around 0.266667</result>