CBSE NCERT Solutions Chapter 5 Arithmetic Progressions Exercise 5.2 Question 20
20. Ramkali saved Rs. 5 in the first week of a year and then increased her weekly savings by Rs. 1.75. If in the nth week , her weekly savings become Rs 20.75, find n.
Ramkali saved Rs. 5 in the first week of year.
It means first term = a = 5
Ramkali increased her weekly savings by Rs 1.75
Therefore, common difference = d = Rs 1.75
Money saved by Ramkali in the second week = a+d = 5 + 1.75 = Rs 6.75
Money saved by Ramkali in the third week = 6.75 + 1.75 = Rs 8.5
Therefore, it is an AP of the form: 5, 6.75, 8.5, ..., 20.75
We want to know in which year her weekly savings become 20.75.
Using formula , to find nth term of arithmetic progression, we can say that
It means in the 10th week her savings become Rs 20.75.