Question

Ramkali saved $Rs.5$ in the first week of a year and then increased her weekly saving by $Rs.1.75$. If in the $n^{th}$ week, her weekly savings become $Rs.20.75$, find $n$.

Answer 1

$\text{Given that},a=5\left(\text{First week saving}\right)d=1.75\left(\text{Weekly saving}\right)a_n=Rs.20.75n=?a_n=a+(n-1)d\Rightarrow 20.75=5+(n-1)\times 1.75\Rightarrow 15.75=(n-1)\times 1.75\Rightarrow (n-1)=\frac{15.75}{1.75}=\frac{1575}{175}\Rightarrow n-1=\frac{63}{7}\Rightarrow n-1=9\Rightarrow n=10\text{Hence},n\text{is}10.$