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If Rita receives $40.04 interest for a deposit earning 5% simple interest for 30 days,
what is the amount of her deposit? (Round your answer to the nearest cent.)
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Use the formula for the simple interest
I = P*r*t.
In this formula, I is the interest, which the principal P produces in t years,
if the annual interest rate is r (decimal value).
In your problem, I = 40.04 dollars (given); P is unknown (principal);
t = 30 days (= 30/365 of a year) and r = 0.05.
So, you have this equation
40.04 = .
From this equation, you find
P = = 9743.07 (rounded to the nearest cent). ANSWER
Solved.
Notice that the final answer DEPENDS on how you count 30 days.
You may count them as 1/12 of a year or as 30/365 of a year - the result will be different.
In order for the resulting number would be unique, the problem MUST INSTRUCT the reader
on how to count 30 days.
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To see many other similar (and different) solved problems on simple interest accounts, look into the lesson
- Simple interest percentage problems
in this site.
Learn the subject from there.