Class 10

Math

All topics

Arithmetic Progressions

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 $n$.

$a_{n}=a+(n−1)d$

Subsituting the values in above equation,

$20.75=5+(n−1)×1.75$

$15.75=(n−1)(1.75)$

$15.75=(n−1)(1.75)$

$⇒n−1=1.7515.75 $

$⇒n−1=9$

$⇒n=10$

$n=10$.

$n=10$.