<image>In order to implement the "Three-life Education" proposed by the Yunnan Provincial Department of Education, on the occasion of Mother's Day, the school's Youth League Committee organized an educational activity with the theme "Cherish Life, Learn to Survive, Be Grateful to Parents," and conducted a random survey among 50 students on the average time they spend doing housework at home each week. The data was summarized and presented in the following frequency distribution and pie chart:
\frac{}According to the above information, answer the following questions:
(1) a=______, b=______;
(2) In the pie chart, the degree of the central angle of group B is______ degrees;
(3) The school has a total of 2000 students. Estimate the number of students in the school who spend at least 4 hours doing housework each week.
