In an office with 40 officers, the average salaries of class-A, class-Band 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 the 40 of them taken together. [Assume the number of days in a month to be 30.]

21,000

Ratio of class A , class B & class C are in ratio = 5 : 4 : 1

10R = 40 ⇒ 1R = 4

Number of officers in class A = 5×4 = 20 , Number of officer in class B = 16 , Number of officer in class C = 4

Monthly income of officers of class A = 20 × 600 × 30 = 3,60,000

Monthly income of officers of class B = 16 × 750 × 30 = 3,60,000

Monthly income of officers of class A = 4 × 1000 × 30 = 1,20,000

Average of income of all 40 officers = \(\frac{360000 + 360000 + 120000}{40}\)

= \(\frac{840000}{40}\) = 21000