∴{ 45x+30( 10-x)≥420
0≤x≤ 10, and the solution is 8≤x≤ 10.
∴x=8,9, 10
There are three car rental schemes.
① Rent 8 buses and 2 CMB buses;
② Rent CMB No.9 bus and 1 bus;
③ Rent 10 bus.
(2)y = 800 x+500( 10-x)= 300 x+5000(8≤x≤ 10)
∫y = 300 x+5000 is a linear function, and y increases with the increase of x.
When x is 8, y is the smallest.
Y=300×8+5000=7400 yuan.
Answer: Rent No.8 bus and CMB No.2 bus. The minimum rent is 7,400 yuan.