Xiao Ming joined the school's basketball team. After a period of training, his shooting percentage was 50% at the lowest and 75% at the highest. Now, what is the minimum number of shots he needs to make to guarantee 15 or more shots?
小明参加了学校的篮球队，经过一段时间的训练，他的投篮投中率最低是50%，最高为75%．现在，如果要保证投中15个球及以上，他最少要投篮多少次？
<gadget id="calculator">75 / 100</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">15 / (3/4)</gadget>
<output>20</output>

<result>20</result>