A person invested ₹12,000 on simple interest for 7 years to obtain a total amount of ₹20,400 on a certain annual rate of interest. What was the rate of interest to obtain the above amount?

10%

Principal( P)  = 12000 Rs

Rate (R%)    =  R% 

Time ( T )      =     7 years

Amount =  20400  Rs

Interest = Amount -  Principal  = 20400- 12000 = Rs 8400

⇒ 8400 = \(\frac{12000 ×Rate × 7 }{100}\)

⇒ \(\frac{8400 ×100 }{12000 × 7 }\) = R %

⇒  Rate = 10% p.a