Answer is: (b) 20%
Let the number of male and female employees be M and F respectively. Then,
Total salary of male employees = Rs 5200 M
Total salary of female employees = Rs 4200 F
Total number of employees = M + F
∴ Total salary of all the employees = Rs 5000 (M + F)
∴ 5200M + 4200F = 5000M + 5000F
⇒ 200M = 800F ⇒ \(\frac{M}{F}=\frac{4}{1}\) ⇒ M : F = 4 : 1
∴ Percentage of female employees = \((\frac15\times100)\) % = 20%