I own a large truck, and my neighbor owns four small trucks that are all identical. My truck can carry a load of at least 600 pounds more than each of her trucks, but no more than 1/2 of the total load her four trucks combined can carry. Based on these facts, what is the greatest load I can be sure that my large truck can carry, in pounds?
Let the load that the small trucks be equal to a variable, small_load. Let the load that the large truck can carry be large_load.
By the statements:
large_load >= small_load + 600
large_load <= (small_load)*4/2 = 2(small_load)
Thus, 2(small_load) >= large_load >= small_load + 600, so 2(small_load) >= small_load + 600
Thereafter, small_load >= 600.
Plugging it into the upper-bound inequality:
large_load <= 2(small_load) = 2(600) = 1200 pounds.