A parallel electric circuit contains four resistors with resistances … | Math SAT Question

A parallel electric circuit contains four resistors with resistances of

p

ohms,

q

ohms,

s

ohms, and 13 ohms. The given equation relates the resistance

R

, in ohms, of the circuit, to the resistances of the four individual resistors it contains. Which equation correctly expresses

R

in terms of

p

q

, and

s

R = \frac{13 pq s}{p + q + s + 13}

R = \frac{13 pq s}{13 q s + 13 p s + 13 pq + pq s}

R = \frac{13 q s + 13 p s + 13 pq + pq s}{13 pq s}

R = p + q + s + 13