If X is invested in a bank at a rate of simple interest of y% p.a. for two years, then the interest earned is 800. if X is invested at y% p.a., for two years when the interest is compounded annually, the interest is 820. What is the value of X?
Choices
A) 8000 B) 6000 C) 5000 D) 4000 E) 3000
Simple way to solve this question is to use options.   From SI, we know that X*y=40,000.   Now, put the value of X = 8000, we will have y = 5%   To calculate CI,   Now, we know 1st year Amount= 8000+5% of 8000= 8400.   2nd year, Amount = 8400 + 5% of 8400 = 8820.   We can see after 2 years Interest = 8820-8000= 
<gadget id="calculator">8820-8000</gadget>
<output>820</output>
820. hence, it satisfies the question. Hence 8000 is the correct answer
<result>A</result>
If X is invested in a bank at a rate of simple interest of y% p.a. for two years, then the interest earned is 800. if X is invested at y% p.a., for two years when the interest is compounded annually, the interest is 820. What is the value of X?