Cost of five carts 1800 yuan. Four cars, three cars, 2040 yuan, three cars, four cars 1880 yuan, two cars, seven cars, 2 120 yuan, and one car, nine cars, 2 160 yuan. So it can be concluded that the five big cars are more economical.

Primary school mathematics is an important subject in compulsory education. From an early age, lay a good foundation for students in mathematics, develop their thinking ability, cultivate their innovative consciousness, practical ability and interest in learning mathematics, and form good study habits.