Question

Part 7c... find the factor by which the electrostatic force will be multiplied if the indicated changes are made. Use formula F= K |q1| |q2| / r^2

Answer 1

Since the force is proportional to the product of charges, the increase by 25% will increase the force by 25%, decreasing the other by 25% will decrease the force by 25%.
The force is inversely proportional to the square of the distance. So decreasing the distance by 20% (Factor of 0.2) increases the force by a factor of
(1/0.8)² = 1.5625