0≤x≤9 ( 1)
1≤y≤9 (2)
It is also derived from known conditions
x+y= 10 (3)
2x+2 & lt; ( 1/2)y (4)
The solution of simultaneous (1)(2)(3)(4) is x= 1 and y=9, so this two-digit number is 19.
2. 1. It takes x hours to set up two factories, A and B, and treat garbage at the same time.
Then we can get (55+45)x=700 x=7 (hours) according to the known conditions.
In the factory, it takes y hours to dispose of garbage every day.
Then there is an inequality group 700≤55y (1).
550y≤7370(2)
The simultaneous solution of (1)(2) is y= 13 (hours).