A certain sum amount to $1400 in 2 yrs and $2000 in five years on certain fixed simple interest. In how many yrs would the amount be $2040 had it been put at the rate of interest compounded annually?
Choose one:  A) 5  B) 4  C) 3  D) 2  E) 1
We can form equations as following:   Initial amount = P, Total amount after interest = T, Interest per year = I   T = P+I   Given T1 = P+2I = 1400T2 = P+ 5I = 2000   From this we get, P = 1000I = 200 $   Now we know that simple interest is&lt;Compound interest ( CI = SI only after 1st year if CI is compounded annually)   consider simple interest - after 1st yer it is 200$ , after 2nd years it is 400$ , after 3rd year it is 600$.and after 4rd year it is 800$.   To get a 640 $ compound interest the duration have to be &gt; 2 year and &lt; 4 years.   Only option fitting : Option 3.
<result>C</result>
A certain sum amount to $1400 in 2 yrs and $2000 in five years on certain fixed simple interest. In how many yrs would the amount be $2040 had it been put at the rate of interest compounded annually?