Explanation

(c)
It will take 10yr for Jairam to pay off Rs 10000 in 10 yearly installments.
$\therefore\ \$He pays 10% annual interest on remaining amount.
$\therefore\ \$Money given in the first year
$= 1000 + \frac{10000 \times 10}{100} = 1000 + 1000$
$= Rs\ 2000$
Money given in second year
$= 1000 + interest\ of\ (10000 - 1000)$
$= 1000 + \frac{9000 \times 10}{100} = 100 + 900 =$ Rs 1900
Similarly, money paid in third year = Rs 1800 etc.
So, money given by Jairam in 10 yr will be Rs 2000, Rs 1900, Rs 1800, Rs 1700 …
Which is in arithmetic progression, whose first term
$a = 2000$ and $d = - 100$
Total money given in 10 yr
$= \frac{10}{2}\left\lbrack 2(2000) + (10 - 1)( - 100) \right\rbrack =$ Rs 15500
Therefore, total money given by Jairam
$= 5000 + 15500 = \$Rs 20500