In an office with 40 officers, the average salaries of class-A, class-B and class-C officers are ₹600, ₹750 and ₹1,000 a day, respectively. The numbers of class-A, class-B, and class-C officers in the office are in the ratio 5 : 4 : 1, respectively. Find the monthly average salary (in ₹) of an officer, all 40 of them taken together. [Assume the number of days in a month to be 30.]

In an office with 40 officers. The numbers of class-A, class-B, and class-C officers in the office are in the ratio 5 : 4 : 1, respectively.

Let's assume the number of class-A, class-B, and class-C officers in the office are 5y, 4y and y respectively.

5y+4y+y = 40

10y = 40

y = 4

the average salaries of class-A, class-B and class-C officers are ₹600, ₹750 and ₹1,000 a day, respectively.

Total salaries of class-A, class-B and class-C officers in a day = $$5y \times600+4y \times750+y \times1000$$

= $$3000y+3000y+1000y$$

= 7000y

Put the value of 'y'.

= $$7000\times4$$

= 28000

Total salaries of class-A, class-B and class-C officers in a month = $$28000\times30$$ = 840000

Monthly average salary (in ₹) of an officer, all 40 of them taken together = $$\frac{Total\ salaries\ of\ all\ the\ officers\ in\ a\ month}{number\ of\ offiers}$$

= $$\frac{840000}{40}$$

= 21000