(1) solution: let the mechanical class be x and the design class be y, then x+y= 150, Y >；; =2x .
If the salary to be paid is the least, then 6000x+ 10000y is the smallest, then x is the largest and y is the smallest, then x=50 and y= 100.
Total salary: 6000 * 50+10000 *100 =1300000 (yuan)
(2) The design bonus is A yuan, and the mechanical bonus is B yuan.
2000 = & ltb = & lta
50b+ 100a=2000000
Therefore, when b=2000, the maximum value of a is a= 19000.
When b=a, the minimum value of a = 13330.33. ....
So 13330.33 =