Question

find the rate of interest if a sum of money becomes 4 times as much in 20 years​

Answer 1

Rate =( x×202x×100 )%p.a.=10%p.a.02-Feb-2021

Answer 2

Step-by-step explanation:

Let the sum be Rs. 1

The sum become after 20 years = 4 × 1 = Rs. 4

SI = 4 – 1 = Rs. 3

As we know,

SI = Prt/100

⇒ 3 = (1 × r × 20) /100

⇒ r = 3 × 5

∴ r = 15%

Short Trick:

Let sum be 100%

SI in three years = 300%

Interest rate for 1 year = 300/20 = 15%