Xiaoxiao has a roll of 15m long ribbon. When she folds Lucky Star, she first uses 1/3 of the full length of the ribbon, and then uses 2/5 of the full length of the ribbon. How much m is the remaining ribbon?
笑笑有一卷长15m的彩带，她折幸运星先用去彩带全长的(1/3)，又用去彩带全长的(2/5)，还余彩带多少m．
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

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

<gadget id="calculator">15 * (4/15)</gadget>
<output>4</output>

<result>4</result>