.
I read and understand the condition differently:
In the first day the shop charges 15 rupees, in the 2-nd day it charges 15+2 = 17 rupees,
in the third day it charges 17+2 = 19 rupees . . . and so on.
What is a bill after "n" days ?
So, it is about finding the sum of the arithmetic progression
15, 17, 19, . . . 15+2(n-1).
The first term is 15, the common difference is 2, and the number of terms = number of days = n.
The answer is: the balance, i.e. the sum of n terms, is = = = = (14+n)*n.
Solved.
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On arithmetic progressions, see the lessons in this site:
- Arithmetic progressions
- The proofs of the formulas for arithmetic progressions
- Problems on arithmetic progressions
- Word problems on arithmetic progressions
- Mathematical induction and arithmetic progressions
- One characteristic property of arithmetic progressions
- Solved problems on arithmetic progressions
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