when a wire is stretched the volume remains the same hence
A1l1=A2l2
From this we get that as the wire's length is doubled the cross sectional area(A) gets halved. So according to: r= row l/A the resistance becomes four times.i.e.60 ohms
But then when it is cut into two halves A remains the same but length gets halfved. So the resistance of the two wires reduce to half.i.e.30 ohms each
When these two equal resistances are connected in parallell the net resistance comes out to be 15.ohms Further we can use ohms law to get the answer.
A1l1=A2l2
From this we get that as the wire's length is doubled the cross sectional area(A) gets halved. So according to: r= row l/A the resistance becomes four times.i.e.60 ohms
But then when it is cut into two halves A remains the same but length gets halfved. So the resistance of the two wires reduce to half.i.e.30 ohms each
When these two equal resistances are connected in parallell the net resistance comes out to be 15.ohms Further we can use ohms law to get the answer.