You can assign up to 50% extra manpower to work, but each worker, being unskilled, is only 25% (0.25) as effective. (i.e. You can boost resource production by 12.5% [0.125]).
In terms of workers:
Take the maximum normal amount of workers and multiply it by 1.5 (150% increase) to get your new maximum amount of workers.
In terms of resources:
Take the normal maximum amount of workers and multiply it by 0.5 (50% or 1/2 increase) to get the maximum added workers and then take that number and multiply it by 0.25 (25% or 1/4) production, which = Original production * (50% * 25% = 12.5% ) = Original production * .125 equals how much goods they will produce.