Question 1105355
<br>
If the monthly deposit amount is rs. 3600 and the interest is simple interest at 9% per year, then the amount of interest on each deposit each month is
rs. 3600*(.09/12) = rs. 27<br>
If n is the number of deposits that are made, then the total amount of interest earned on the first deposit is 27(n); the total amount of interest on the second deposit is 27(n-1);...; the total amount of interest on the next-to-last deposit is 27(2), and the total amount of interest on the last deposit is 27(1).<br>
Then the total amount of interest on all the deposits is
27(n+(n-1)+...+2+1) = 27*((n(n+1)/2)<br>
Since the total amount of interest is rs. 17982,
{{{27(n(n+1)/2) = 17982}}}
{{{n(n+1) = 2*17982/27 = 1332}}}<br>
Any of various methods will lead to {{{36*37=1332}}}, so the number of deposits n is 36.