physics
posted by capacitance q .
According to its design specification, the timer circuit delaying the closing of an elevator door is to have a capacitance of 30.0 µF between two points A and B.
(a) When one circuit is being constructed, the inexpensive but durable capacitor installed between these two points is found to have capacitance 33.6 µF. To meet the specification, one additional capacitor can be placed between the two points. Should it be in series or in parallel with the 33.6 µF capacitor?
in series
in parallel
What should be its capacitance?
µF
(b) The next circuit comes down the assembly line with capacitance 29.3 µF between A and B. What additional capacitor should be installed in series or in parallel in that circuit, to meet the specification?
in series
in parallel
µF

Capacitors in series subract.
Capacitors in parallel add.
#2.
!/c = 1/c1 + 1/c2
You know c and c2, substitute and solve for c2.