Question

<!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}--> (i) At what rate per cent per annum will Rs. 630 produce an interest of Rs. 126 in 4 years?
(ii) At what rate per cent per year will a sum double itself in $6\frac{1}{4}$ years?

Answer 1

<!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}--> (i) $P=$ Rs. $630,I=$ Rs. $126,T=4$ years
$$R=\frac{100\times 1}{P\times T}=\frac{100\times 126}{630\times 4}=\frac{100}{20}=5\%$$
(ii) Let $P=$ Rs. 100
$\therefore$ Amount $=2\times$ Rs. $100=$ Rs. 200
Interest $=A-P$
$=$ Rs. $200-$ Rs. $100=$ Rs. 100
$T=6\frac{1}{4}$ years $=\frac{25}{4}$ years
$$R=\frac{100\times 1}{P\times T}=\frac{100\times 100}{100\times \frac{25}{4}}\%=\frac{100\times 100}{100}\times \frac{4}{25}=16\%$$