A mathematical problem A company is planning to organize some employees to travel to Beijing in May. Now it has contacted two travel agencies, a and B. both travel agencies offer a price of 2000 yuan per person. At the same time, both travel agencies offer preferential measures to groups with more than 10 employees: a travel agency gives 25% discount to each employee; B travel agency exempts one leader from the cost of managing employees, and the rest employees get 20% discount (1) If there are a (a > 10) employees participating in the tour, the cost of travel agency a is () The cost of B travel agency is () yuan (2) If the company now organizes 20 employees including management staff to travel to Beijing, which travel agency will be more favorable for the company? Please explain the reason. (explain the reason) 3. If we plan to travel for seven days in May, let the date in the middle be a, then the sum of the dates of the seven days is () (expressed by an algebraic expression containing a and simplified) If the sum of these seven days is a multiple of 63, what date may they start on? (write down all the possibilities that meet the conditions, and write down the simple calculation process)

A mathematical problem A company is planning to organize some employees to travel to Beijing in May. Now it has contacted two travel agencies, a and B. both travel agencies offer a price of 2000 yuan per person. At the same time, both travel agencies offer preferential measures to groups with more than 10 employees: a travel agency gives 25% discount to each employee; B travel agency exempts one leader from the cost of managing employees, and the rest employees get 20% discount (1) If there are a (a > 10) employees participating in the tour, the cost of travel agency a is () The cost of B travel agency is () yuan (2) If the company now organizes 20 employees including management staff to travel to Beijing, which travel agency will be more favorable for the company? Please explain the reason. (explain the reason) 3. If we plan to travel for seven days in May, let the date in the middle be a, then the sum of the dates of the seven days is () (expressed by an algebraic expression containing a and simplified) If the sum of these seven days is a multiple of 63, what date may they start on? (write down all the possibilities that meet the conditions, and write down the simple calculation process)

1. A 2000a * 75% = 1500A, B (2000a-2000) * 80% = 1600a-1600 = 1600 (A-1) 2. A 1500A = 1500 * 20 = 30000 yuan, B 1600 (A-1) = 1600 * 19 = 30400 yuan. Obviously, choose a 3.7a 1 times 7a = 63 A = 9 9-3 = 6 2 times 7a = 63 * 2 a = 18 18-3 = 15 times 7a = 63 * 3 a = 27-3 = 2