Question

R=10 ohms and r1 =20 and r2 =40 what is the r3

Answer 1

Answer:

Total R = 10 ohms

Since the resistors seems to be connected in parallel

∴ 1/R = 1/r1 + 1/r2 + 1/r3

⇒ 1/10 = 1/20 + 1/40 + 1/r3

    [let r3 = x]

⇒ 1/10 = $\frac{2x + 3x + 40}{40x}$

⇒ $\frac{40x}{10}$ = 5x + 40

⇒ 40x = 50x + 400

⇒ -10x = 400

⇒ x = 40 ohms