On a sum invested at compound interest, the interest credited for the second year is ₹1320 and the interest credited for the third year is ₹1452. The sum invested (in ₹) was:

Each year's interest is the previous year's interest grown by the rate, so 1452/1320 = 1.10 gives $r=10$%. The second year's interest is earned on the first year's amount: $1320=P\times 1.10\times 0.10=0.11P$ → $P$ = ₹12000. (Year by year: 12000 → 13200 → 14520 → 15972, with interest 1200, 1320, 1452.)