.
Interest I = D*r*t, (1)
where D is the original deposit amount, r is the rate, expressed as decimal, and t is time in years.
In this problem, r = 0.045, r = 18 months = 1.5 years.
So, the equation (1) takes the form
90 = D*0.045*1.5,
which gives the ANSWER D =
= 1333.33 dollars.
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To see other similar solved problems and to feel a solid ground under your legs, look into the lesson
- Simple interest percentage problems
in this site.