There is a barber in a barber shop, and three customers A, B, and C come at the same time. A said: "I only cut it, it takes 10 minutes"; B said: "I cut it, but I have to wash it, it takes 15 minutes"; C said: "I want to cut, wash, and blow it, it takes 20 minutes". How to arrange to minimize the waiting time for the three of them?
理发店有一位理发师，同时来了甲、乙、丙三位顾客．甲说："我只剪，需要10分钟"；乙说："我剪了，还要洗，需要15分钟"；丙说："我要剪、洗、吹，需要20分钟"．怎样安排使他们三人等候的时间最少？
<gadget id="calculator">10 * 3</gadget>
<output>30</output>

<gadget id="calculator">15 * 2</gadget>
<output>30</output>

<gadget id="calculator">30 + 30 + 20</gadget>
<output>80</output>

<result>80</result>