Why are most factors held constant in an experiment?

Often called simply "velocity," this is the velocity of an object at a particular moment in time.

If element x has 99 protons how many electrons does it have

Two pans of a balance are 24.1 cm apart. the fulcrum of the balance has been shifted 1.33 cm away from the center by a dishonest shopkeeper. by what percentage is the true weight of the goods being marked up by the shopkeeper? assume the balance has negligible mass. answer in units of %.