Equivalent Capacitance, physics?

Question

Two capacitors are connected to each other in series as shown in the figure. The values of the capacitances are the following: C1 = 2.02 nF, C2 = 4.38 nF. What is their equivalent capacitance?

Answer 1

Figure? -----||-----||----- Like that?

If so, 1/Ct = 1/C1 + 1/C2

This can be re-written
1/Ct = (C2 + C1) / C1C2
Ct = C1C2 / (C1+C2)

This is often said as "product over sum"
"product over sum" works with resistors in parallel too.