At what annual rate of interest will a sum of money be thrice in 10 years?

Question: At what annual rate of interest will a sum of money be thrice in 10 years?

Solution:
Amount = Principal + SI
If the sum of money would be thrice the principal after 10 years, the SI would be twice the principal.
⇒ SI = 2 × P
⇒ (P × R × T / 100) = 2 × P
⇒ R × T / 100 = 2
⇒ R × T = 200
⇒ R × 10 = 200
⇒ R = 20%
Thus, the required rate of interest is 20%