document.write( "Question 643216: A simple-interest account contained $780 eight months after it was opened, and it contained $855 ten months after that. Find the original amount in the account.
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Algebra.Com's Answer #404387 by Theo(13342)\"\" \"About 
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simple interest means no compounding.
\n" ); document.write( "this means your interest per month is going to be the same every month.
\n" ); document.write( "the formula for simple interest is:
\n" ); document.write( "f = p * i * n
\n" ); document.write( "i is the interest rate.
\n" ); document.write( "p * i is the interest
\n" ); document.write( "p is the principal.
\n" ); document.write( "f is the future value.
\n" ); document.write( "n is the number of time periods.
\n" ); document.write( "just solve for the monthly interest and work your way back.
\n" ); document.write( "in your problem:
\n" ); document.write( "account contains 780 after 8 months and contains 855 10 months after that.
\n" ); document.write( "in 10 months, the account grew from 780 to 855 which is a growth of 75 dollars.
\n" ); document.write( "divide that by 10 months and that becomes 7.5 dollars growth per month.
\n" ); document.write( "8 * 7.5 = 60 dollars.
\n" ); document.write( "subtract 60 from 780 and you start with 720 dollars 8 months before you had 780.
\n" ); document.write( "your original amount is 720 dollars.
\n" ); document.write( "your interest per month is 7.5
\n" ); document.write( "720 + 8*7.5 = 780 + 10*7.5 = 855.
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