Why does placing resistors in parallel decrease the resistance?
There's a waterfall pushing 600 gallons per second. You divert a small section through a small water hose giving you 5 gallons per second. Your current is 5 gallons per second. 

Add another of the same size hose. You more have 2 currents that add up to 10 gallons per second. 

It's like a single hose that does 10 gallons per second. 

This is an approximation of how parallel resistors work.