Two persons A and B started working for a company in similar jobs on January 1, 1990. A's initial monthly salary was Rs 400, which increases by Rs 50 after every year. B's initial monthly salary was Rs 500 which increases by Rs 20 after every six months. If these arrangements continue till December 31, 1994. Find the total salary they received during that period.

. A's salary as of 1 Jan 1990 is Rs 400 per month. His increment in his monthly salary is Rs 50 per annum. His total salary from 1 Jan 1990 to 31st Dec 1994 By the formula of AP S = n/2 [2a + (n-1) d], where n = 5 years, a = 400 and d = 50 =12[2(400) +(5−1)50] ×5/2 =12×2500 =Rs 30000 B's salary as of Jan 1st, 1990, is Rs 500 and his half-yearly increment in his monthly salary is Rs 20. His total salary from 1 Jan 1990 to Dec 31, 1994 = 2[2(500) +(10−1)20] ×10/2 =2× [1000+180] ×5 =2×5900 =Rs 11800 Since these are monthly salaries, we need to multiply by 6 (since it is bi-annual): Total salary of B over 5 years=11800×6=35400 Total salary of A and B in the 4-year period: = Rs. 30000 + Rs. 35400 ⇒ Rs 65400