A sum of money lent out at S.I. amounts to a total of $520 after 2 years and to $820 after a further period of 5 years. What was the initial sum of money that was invested?
Select: A) $340 B) $360 C) $380 D) $400 E) $420
S.I for 5 years = $820 - $520 = $300   The S.I. is $60/year   S.I. for 2 years 820 -  520= 
<gadget id="calculator">820 -  520</gadget>
<output>300</output>
$300   The S.I. is $60/year   S.I. for 2 years= $120   Principal = $520 - $120 = $400   The answer is $400.520 -  120= 
<gadget id="calculator">520 -  120</gadget>
<output>400</output>
$400   The answer is $400.
<result>D</result>
A sum of money lent out at S.I. amounts to a total of $520 after 2 years and to $820 after a further period of 5 years. What was the initial sum of money that was invested?