Question
In the figure below, the ammeter A reads 0.3 A. Calculate: 
i) the total resistance of the circuit.
ii) the value of R.
iii) the current flowing through r.
Solution
i) We know, V = IR
ii) Total resistance, R = 20 ohm
Therefore,
Resistors are in parallel. 
iii) We know that,
V = IR
Potential (V) is equal at the two ends.
Let, I1 be the current flowing through R and I2 be through 60 ohm.
I1 + I2 = 0.3
I2=(0.3-I1)
Now, we have V=V
That is,
I1R1 = I2R2
I1 x 30= (0.3-I1) x 60
I1 = 0.6 – 2I1
3I1=0.6
Therefore,
Current flowing through R = 0.2 A
