Question

at what rate percent compund interest per annum will RS 640 amount to RS 774.40 in 2 years .

Answer 1

Imagine that the rate of percent per annum is r%
so in 2 years RS 640 will amount to RS 774.40

hence , at r% rate annum interest the compound interest including the main price is ------
= 640(1+r/100)^2 RS
According to the question....
$640 {(1 + \frac{r}{100} )}^{2} = 774.40 \\ or \: \: {(1 + \frac{r}{100}) }^{2} = \frac{774.40}{640} \\ or \: \: {(1 + \frac{r}{100}) }^{2} = \frac{77440}{64000} \\ or \: \: {(1 + \frac{r}{100} )}^{2} = \frac{7744}{6400} \\ or \: \: (1 + \frac{r}{100} ) = \frac{88}{80} \\ or \: \: (1 + \frac{r}{100} ) = \frac{11}{10} \\ or \: \: \frac{r}{100} = \frac{11}{10} - 1 \\ or \: \: r = \frac{1}{10} \times 100 \\ or \: \: r = 10\%$
so the rate of percent per annum is 10%.
hope it helps, please mark it brainliest..

Answer 2

$\large\sf\bullet{\; Check\: Attachment}$