Sum invested = P = Rs. 1000
Rate of interest = R = 8%
Time of investment = 1 year
∴ Amount of interest (simple)
So the amount of interest for the years 1, 2, 3, …………….are
80, 160, 240,….. are in an A.P.
In which the first term (a) 5= 80
Common difference (d) = a2 – a1
= 160 – 80 = 80
∴ The amount of interest to be paid in 30 years of time = S30
Sn = j [2a + (n- l)d]
= \(\frac{n}{2}\) [2(80) + (30 – 1) 80]
= 15[160 + 29(80)]
= 15[160 + 2320]
= 2480 × 15 – Rs.37200
∴ Rs.37200 will be paid towards interest for 30 years.