This is one of my pet peeves too:
People often think that if you decrease something by 50% then increase it by 50% you end up with the original value. It’s surprisingly difficult for people to grasp this is not true. I found it works better if you use 100% reduction followed by a 100% increase. When they say, “But that is different.” I just walk away to avoid the nearly irresistible urge to do some minor cleaning of the gene pool.