How Do You Calculate the Capacitance of a Second Capacitor in Parallel?

[wushumaster]

A 100 pF capacitor is charged to a potential difference of 50 V, and the charging battery is disconnected. The
capacitor is then connected in parallel with a second (initially uncharged) capacitor. If the potential
difference across the first capacitor drops to 35 V, what is the capacitance of this second capacitor?

I am totally stuck! Please help! I know the voltage of both will be the same..

 

[gneill]

Why do you think the voltage across the first capacitor dropped from 50V to 35V?

 

[Jiggy-Ninja]

I shall give you three hints.

1) $$Q\ =\ C\ \times\ V$$

2) For capacitors connected in parallel: $$C_{T}\ =\ C_{1}\ +\ C_{2}\ +\ C_{3}\ + ...$$

3) Charge is always conserved.