A man starts his job with a certain monthly salary and earns afixed increment every year. If his salary was Rs. 1500 after 4 years ofservice and Rs. 1800 after 10 years of service what was his startingsalary and what is the annual increment?.

Let the man's starting salary be Rs. x and his annual increment be Rs. y
Condition 1:
His salary after 4 years of service is Rs. 1500
x + 4y = 1500… (i)
Condition 2:
His salary after 10 years of service is Rs. 1800
x + 10y = 1800… (ii)
Subtracting (i) from (ii)
x + 10y = 1800
x +   4y = 1500
(-)   (-)    (-)
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6y =  300
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y =  300/6
y = 50
Substitute y = 50 in (i)
x + 4 (50) = 1500
x + 200 = 1500
x = 1500 - 200
x = 1300
. ^. . The man's starting salary is Rs. 1300 and his annual increment is Rs. 50.
Verification:
(a) Man's salary after 4 years   = 1300 + 4(50)  =  1300 + 200 = Rs. 1500
(b) Man's salary after 10 years = 1300 + 10(50) = 1300 + 500 = Rs. 1800.