An article can be bought by paying ₹28000 at once or by making 12 monthly installments. If the first installment paid is ₹3000 and every other installment is ₹ 100 less than the previous one, find :

(i) amount of installment paid in the 9^th month.

(ii) total amount paid in the installment scheme.

(i) a₉ = a + 8d

= 3000 + 8(-100)

= 3000 - 800

= 2200.

Hence, amount of installment paid in the 9^th month = ₹ 2200.

(ii) Total amount paid in the installment scheme,

$= \dfrac{n}{2}[2a + (n - 1)d] \\[1em] = \dfrac{12}{2}[2 \times 3000 + (12 - 1) \times (-100)] \\[1em] = 6[6000 - 1100] \\[1em] = 6 \times 4900 \\[1em] = 29400.$

Hence, total amount paid in the installment scheme = ₹ 29400.