A machine bought for ₹60000 loses ₹4500 of its value every year. What is its value at the end of 8 years?

**Salaries**: 'Person earns ₹X in year 1 with annual increase of ₹Y. Find salary in year n / total over n years.' → AP with a = X, d = Y.

**Stadium seating**: 'Front row has 30 seats; each row 4 more. 25 rows. Total seats?' → AP with a = 30, d = 4. S₂₅ = ?

**Loans/installments**: equal monthly payments form an AP.

**Number patterns**: 'Multiples of 5 between 100 and 500: how many? Sum?' → AP with a = 100, d = 5, last = 500.

Always identify a, d, and what's asked (term aₙ or sum Sₙ). Check whether n is the COUNT or the POSITION.