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# Help

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A savings account at Xyz Bank offers 4% interest, compounded annually. How much money must I invest today in order for the account to grow to  in ten years? Answer to the nearest whole dollar.

The bacteria in a jar triple every 20 seconds. After three minutes, there are 275,562 bacteria in the jar. How many were in the jar at the beginning of the experiment?

At the beginning of each year, Joe invests \$10,000 in his retirement fund. The fund gives 10% interest, compounded annually. At the end of the third year, how much money will be in Joe's fund?

Kevin borrowed \$2000 from his mother at an interest rate of 5%, compounded monthly. How much does he owe (including the original \$2000) at the end of 3 years? Give your answer rounded to the nearest cent.

Five thousand dollars compounded annually at an x% interest rate takes six years to double. At the same interest rate, how many years will it take 300 to grow to 9600?

Apr 9, 2019

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The bacteria in a jar triple every 20 seconds. After three minutes, there are 275,562 bacteria in the jar. How many were in the jar at the beginning of the experiment?

Three minutes = 180 seconds

We have this

A = A0(3)^[ ( t / 20 )       where  A0  = the original number.....A is the number after t seconds

Filling in what we know.....

275562 = A* 3^(180/20 )

275562 = A0 * 3^(6)           divide both sides by 3^6

275562 / 3^6   =  A0  =  378   Apr 9, 2019