如图所示，小灯泡的电阻为10Ω，滑动变阻器R的阻值范围为“0～20Ω”，则小灯泡和滑动变阻器串联后电阻的最大值是 ____Ω；闭合开关后，变阻滑片由b往a移动，小灯泡的亮度 ____（选填“变亮”、“变暗”或“不变”）

It's raining. Ann meets Little Water Drop. She's talking with him.

Ann: Hi, where do you come from, Little Water Drop?

Little Water Drop: I come from the sea.

Ann: Oh，that's far from here.

Little Water Drop: Yes. I come here in a cloud. I fly over rivers and mountains.

Ann: Now you fall down here. How do you go back to the sky?

Little Water Drop: The sun shines and shines. I get hot. Then I go up to the sky. It's cool there. I am in a cloud.

Ann: Do you feel happy?

Little Water Drop: Yes, I do. I can help people. I am useful. People use water to wash clothes and vegetables, cook food, wash clothes, make drinks and so on. Farmers use water to grow crops and firemen use water to put out fires.

现有一堆棋子，把它分成三等份后还剩一颗；取出其中的两份又分成三等份后还剩一颗；再取出其中的两份再分成三等份后还剩一颗．问原来至少有多少颗棋子？