Question 985541
P=principal (original investment); r=interest rate (expressed as decimal); t=time(must match rate time- if rate is 5% per year, time must be in years); I=amount of interest.
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I=Prt Can be solved for any of the variables.
P=I/rt Divide each side by rt.
r=I/Pt Divide each side by Pt.
t=I/Pr Divide each side by Pr.
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To find original investment, P, you must know (or be able to calculate) Interest received (I), interest rate (r), and time invested (t).