Question

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

Answer 1

Given that,
$a = 5$, $d = 1.75$ and $a_n = 20.75$.
$n = ?$
$a_n = a + (n − 1) d$
$20.75 = 5 + (n-1)1.75$
$15.75 = (n-1)1.75$
$n-1 = \frac {15.75}{1.75}$

$n-1 = \frac {1575}{175}$

$n-1 = \frac {63}{7}$
$n − 1 = 9$
$n = 10$

Hence, n is 10.