1. **Problem statement:** Kumar saves money starting with 1 rupee on the first day, 3 rupees on the second day, 5 rupees on the third day, and so on, increasing by 2 rupees each day. We need to find the total amount saved in 20 days, which is the price of the book. 2. **Identify the sequence:** The savings form an arithmetic sequence where the first term $a_1 = 1$ and the common difference $d = 2$. 3. **General term formula:** The $n$th term of an arithmetic sequence is given by $$a_n = a_1 + (n-1)d$$ Substitute $a_1 = 1$ and $d = 2$: $$a_n = 1 + (n-1) \times 2 = 2n - 1$$ 4. **Sum of first $n$ terms:** The sum $S_n$ of the first $n$ terms of an arithmetic sequence is $$S_n = \frac{n}{2} (a_1 + a_n)$$ 5. **Calculate $a_{20}$:** $$a_{20} = 2 \times 20 - 1 = 40 - 1 = 39$$ 6. **Calculate $S_{20}$:** $$S_{20} = \frac{20}{2} (1 + 39) = 10 \times 40 = 400$$ 7. **Conclusion:** Kumar saved a total of 400 rupees in 20 days, so the price of the book is 400 rupees.