At what rate of interest per annum will a sum triple itself in 9 years, if calculated as per simple interest formula.

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Solution

Let the sum invested be P, and the rate of interest be R

Given in 9 years, $A m o u n t = 3 P$

$\Rightarrow P + S I = 3 P$

$\Rightarrow S I = 2 P$
$[0.5 m a r k]$

$\Rightarrow \frac{P \times T \times R}{100} = 2 P$

$\Rightarrow T \times R = 200$

$\Rightarrow R = \frac{200}{T} = \frac{200}{9} = 22.22 %$
$[0.5 m a r k]$

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At what rate of interest per annum will a sum triple itself in 9 years, if calculated as per simple interest formula.

Let the sum invested be P, and the rate of interest be R Given in 9 years, Amount=3P ⇒P+SI=3P ⇒SI=2P [0.5 mark] ⇒P×T×R100=2P ⇒T×R=200 ⇒R=200T=2009=22.22% [0.5 mark]