The following table shows the number of working hours and the number of employees employed in a small scale industry No. of working hours No. of employees 3 - 5 7 5 - 7 10 7 - 9 18 9 - 11 57 11 - 13 14 13 - 15 8 The average number of working hours of an employee is

Answer: Option B

We have :

Mean working hours	4	6	8	10	12	14
No. of employees	7	10	18	57	14	8

Sum of working hours of all the employees
= (4 × 7 + 6 × 10 + 8 × 18 + 10 × 57 + 12 × 14 + 14 × 8)
= (28 + 60 + 144 + 570 + 168 + 112)
= 1082
Total number of employees
= (7 + 10 + 18 + 57 + 14 + 8)
= 114
∴ Average number of working hours
= $$\left(\frac{1082}{114}\right)$$
= 9.49 $$\approx$$ 9.5