Q.Under the same simple interest rate, a principal amount grows to 7000 rupees in 5 years and 8200 rupees in 8 years. What is the rate of interest? (a) 4% (b) 6% (c) 8% (d) 10%
Answer: C
For 3 years \((8-5)\), the interest amount is \((8200-7000)\) rupees = 1200 rupees
\(\therefore\) Interest for 1 year = \(\cfrac{1200}{3}=400\) rupees
\(\therefore\) Interest for 5 years = 400\(\times\)5 rupees

= 2000 rupees

\(\therefore\) Principal amount = (7000-2000) rupees

= 5000 rupees

\(\therefore\) Rate of interest \((r)=\cfrac{100\times I}{pt} \%\)

\(=\cfrac{100\times 2000}{5000\times 5}\%\)

\(=8\%\)

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