1) All sacks of sugar have the same weight. All sacks of flour also have the same weight, but not necessarily the same as the weight of the sacks of sugar. Suppose that two sacks of sugar together with three sacks of flour weigh no more than 40 pounds and that the weight of a sack of flour is no more than 5 pounds more than the weight of two sacks of sugar. What is the largest possible weight (in pounds) of a sack of flour?
I solve this with linear programming (and a little Agebra)
Let x = weight of sack of sugar
Let y = weight of a sck of flour
We have these inequalities
2x + 3y ≤ 40
y - 2x ≤ 5
Set these up as equalities
2x + 3y = 40 (1)
y -2x = 5 ⇒ y = 5 + 2x (2)
Sub (2) into (1) and we have that
2x +3( 5 + 2x) = 40
8x + 15 = 40
8x = 25
x = 25/8 = 3.125 lbs
So...max weight for a sack of flour = 5 + 2(3.125) = 11.25 lbs
See the graph here : https://www.desmos.com/calculator/pjcr7qcxiz
The max for the weight of a sack of flour occurs at (3.125, 11.25)