The question is given from ncert Book of class 10th Chapter no. 5 Ex. 5.2 Q. 20. In the following question you have to find that in which week the saving of Ramkali became Rs 20.75 if she increases her weekly savings by Rs 1.75 every week with the initial saving of Rs 5. Give the solution of the above question.
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Ramkali saved Rs 5 in the 1st week of a year and then increased her weekly saving by Rs 1.75. If in the nth week, her weekly savings become Rs 20.75, Find the value of n.
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Solution:
It is given that, Ramkali saved Rs.5 in 1st week and then started saving Rs.1.75 each week.
Hence,
a = 5
d = 1.75
It is also given,
an = 20.75
n = ?
By the nth term formula,
an = a+(n−1)d
i.e
20.75 = 5+(n -1)×1.75
15.75 = (n -1)×1.75
(n -1) = 15.75/1.75 = 1575/175
= 63/7 = 9
n -1 = 9
n = 10
So, n is 10.