(2) According to the meaning of the question, a set of linear inequality equations can be listed, from which it is concluded that y increases with the increase of x 。
Solution: Solution:
( 1)y = 280 x+(6-x)×200 = 80x+ 1200(0≤x≤6)。
(2) There can be a balance.
{
80x+ 1200≤ 1650
{
45x+30(6-x)≥240
4≤x≤45/8 solution inequality group
The prepaid car rental fee can have a balance.
X is an integer.
∴x needs 4 or 5
∫k = 80 > 0
∴y increases with the increase of x
When x=4, the value of y is the smallest.
The minimum value y=4×80+ 1200= 1520 yuan.
∴ The maximum surplus is1650-1520 =130 yuan.
Answer: Maximum balance 130 yuan.
Comments: The key to solving a problem is to understand the meaning of the problem, find the key descriptors, and then find the equivalence relation of the required quantity. It is the key to solve the problem to find the range of x by using the inequality relationship in the problem and the minimum value of y according to the monotonicity of the function.