SOLUTION: A certain sum doubles in 3 years under simple interest. In how many years will the sum become 5 times itself?

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Question 1096403: A certain sum doubles in 3 years under simple interest. In how many years will the sum become 5 times itself?

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
+I+=+P%2Ar%2At+
After 3 yrs you end up with +I+%2B+P+=+2P+, so
+I+=+P+
----------------
+t+=+3+ yrs
+P+=+P%2Ar%2A3+
Divide both sides by +P+
+1+=+1%2Ar%2A3+
+r+=+1%2F3+
------------------
For the sum to get multiplied by +5+,
+I+%2B+P+=+5P+
+I+=+4P+
and
+4P+=+P%2A%281%2F3%29%2At+
+4+=+%281%2F3%29%2At+
+t+=+12+
In 12 yrs the sum gets multiplied by +5+