Answer:
4. The reading decreases because part of your weight is applied to the table and the table exerts a matching force on you that acts in the direction opposite to your weight.
Step-by-step explanation:
When you push on anything, Newtons Third Law comes into effect: "when two objects interact, they apply forces to each other of equal magnitude and opposite direction." So pretty much, the table you are putting some of your weight on is taking some of the downward force and in return the scale isn't going to push up with as much force.
I'm not the best at explaining, but im in physics right now and thats somewhat how my teacher explained it.