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July 18th, 2019, 04:53 AM   #1
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Why principal is taken as 10 instead of 100?

If the S.I for 6 years be equal to 30% of the principal, it will be equal to the principal after how many years?

Sol:

$\displaystyle → 3 = 10*6*\large\frac{R}{100}$

$\displaystyle → R = 5%$

$\displaystyle → 10 = 10*T*\large\frac{5}{100}$

$\displaystyle → T = 20 yrs$

Why principal is taken as 10 instead of 100?

Last edited by Ganesh Ujwal; July 18th, 2019 at 04:56 AM.
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July 18th, 2019, 06:23 AM   #2
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It doesn't really matter, since that is not necessarily the principal. The important thing is the 3 is 30 % of the 10. You could write it as 30 = 100*6*(R/100).

More importantly, since simple interest is proportional to time,
$\displaystyle \frac{I_1}{T_1} = \frac{I_2}{T_2} \rightarrow T_2 = (\frac{100 \%}{30 \%})(6~years) = 20~years$
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July 18th, 2019, 07:08 AM   #3
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I took the wordy approach:
If we get 30% after 6 years, that's 30%/6years = 5% per year. 100%/5% per year is 20 years
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