Two cells of emf 1.5 V and 2.0 V having internal . . .

Question : Two cells of emf 1.5 V and 2.0 V having internal resistance 0.2 Ω and 0.3 Ω respectively are connected in parallel. Calculate the emf and internal resistance of the equivalent  cell.

Doubt by Saif 

Solution : 

ε₁ = 1.5 V

ε₂ = 2.0 V

r₁ = 0.2Ω

r₂ = 0.3Ω

We know, Equivalent emf when two cells are connected in parallel is given by 
ε_eq = (ε₁r₂+ε₂r₁)/(r₁+r₂)

ε_eq = (1.5×0.3+2×0.2)/(0.2+0.3)

ε_eq = (0.45+0.4)/(0.5)
ε_eq = 0.85/0.5
ε_eq = 1.7 V

Equivalent internal resistance when two cells are connected in parallel is given by 

1/r_eq = 1/r₁+1/r₂

r_eq = r₁r₂/(r₁+r₂)
r_eq = 0.2×0.3/(0.2+0.3)
r_eq = 0.06/0.5
r_eq = 0.12Ω