Problem Solving

I have a problem with habitually making the same mistakes over and over. I keep seeing the same mistakes and make mental notes of the reoccurring mistakes, however I can't seem to stop making them. An example OG PS #127
To mail a package the rate is x cents for the first pound and y cents for each add'l pound, where x > y. Two packages weighing 3 pounds and 5 pounds, respectively, can be mailed separately or combined as one package. Which method is cheaper, and how much money is saved?

Here I picked values, x = 100, 100 and y = 90, 50

100 + 2(50) = 200 3lb and 100 + 4(50) = 300 5lb, 200 + 300 = 500
here is where I made the mistake, combined 100 + 6(50) = 400
Thus 500 - 400 = 100
Combined, with a savings of x cents

The correct answers is 100 + 7(50) = 450
Thus 500 - 450 = 50
Combine with a saving of x - y cents

Another mistake I made, PS # 124

In Town x, 64 percent of the population are employed, and 48 percent of population are employed males. What percent of the employed people in town x are females?

So here I sent up a box,
100 Male Female Total
Employed 48 16 64
Unemployed

So, of course, I choose 16. BUT, it asked for percent so it's actually 16/64 or 25%.

These are the types of mistakes I keep making, even after reading numerous articles on this forum on how to avoid these mistakes and yet I continue to fall into the test makers' traps. Does anyone have any suggestions? I'm about ready to get a tazer gun to shock myself if I do not re-read the stem.