David invested a certain sum of money in a bank that paid simple interest. The amount grew to $300 at the end of 2 years. He waited for another 3 years and got a final amount of $390. What was the principal amount that he invested at the beginning? Choose the correct choice from the following answers: A) $340 B) $300 C) $280 D) $260 E) $240
What shall be the rate of interest.? Does that is not required for the calculation?   Not really!   Keep in mind that the interest earned each year will be the same in Simple Interest.   At the end of 2 years, Amount = $300   At the end of 5 years, Amount = $390   This means she earned an interest of $90 in 3 years. Or $30 in each year.   We know that the interest earned each year will be the same.   Therefore she must have earned $60 in 2 years.   Hence Principal Amount = $300 - $60 = $240 Option $240300 -  60= 
<gadget id="calculator">300 -  60</gadget>
<output>240</output>
$240 Option $240
<result>E</result>
David invested a certain sum of money in a bank that paid simple interest. The amount grew to $300 at the end of 2 years. He waited for another 3 years and got a final amount of $390. What was the principal amount that he invested at the beginning?