# 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's saving in First week = Rs. 5

Ramkali's saving in second week = Ramkali's saving of first week + Ramkali's saving of second week = 5 + 1.75 = Rs. 6.75

Rampkali's saving in third week = 6.75 + 1.75 = Rs. 8.50

And thus an AP will be formed as 5, 6.75. 8.50,......... with common difference of 1.75

Now, Saving in nth week = Rs. 20.75

Therefore,

a = 5, d = 1.75 and an = 20.75

We know, an = a + (n -1)d

20.75 = 5 + (n – 1)1.75

(n – 1) 1.75 = 20.75 – 5

(n – 1) 1.75 = 15.75

n – 1 = 15.75/1.75 = 9

n = 10

So in 10 weeks her savings will be Rs. 20.75

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