Physics.
posted by Amber. .
A 15.0 resistor and a 20.0 resistor are connected in parallel. A 5.00 resistor is connected in series with this parallel arrangement. The resistors are connected across a 1.00 10^2V battery. What is the current flowing through the 20.0 resistor?
IS it 3.15 A?

That's not what I got.
The equivalent resistance of the 20 ohm and 15 ohm resistors in parallel is, in ohms, (20 * 15)/(20 + 15). Add that to the 5 ohm resistor connected in series. Finally divide the applied voltage, 100 volts, by the total resistance to get the current. 
I got it like this :
two in parallel are equal to 15*20/35 = 8.57 ohms
that in series with 5 ohms gives you 13.57 ohms
I = E/R = 100/13.57 = 7.37 amps total current.
voltage across parallel combo is E = IR = 7.37 x 8.57 = 63.1 volts
current through 20 ohms, I = E/r = 63.1/20 = 3.15 
Yes, you're right! I missed the last part that stated "through the 20.0 resistor".
Sorry about that