Two identical current sources are connected in one case in series, in the other case – in parallel and closed

Two identical current sources are connected in one case in series, in the other case – in parallel and closed to an external resistance of 1 Ohm. At what internal resistance of the current source will the current in the external circuit be the same in both cases?

According to Ohm’s law for a complete circuit, the current in the circuit is defined as
I = E / (R + r),
Where
E – EMF of the source,
r is its internal resistance,
R = 1 Ohm – external resistance;
When two sources are connected in series, the total EMF is E1 = 2 * E, and the total internal resistance is r1 = 2 * r;
Respectively:
I1 = E1 / (R + r1) = 2 * E / (R + 2 * r);
When two sources are connected in parallel, the total EMF is E2 = E, and the total internal resistance is r2 = r / 2;
Respectively:
I2 = E2 / (R + r2) = E / (R + 0.5 * r);
According to the condition of the problem:
I1 = I2;
2 * E / (R + 2 * r) = E / (R + 0.5 * r);
2 * (R + 0.5 * r) = R + 2 * r;
r = R = 1 ohm.