3. $6125 at 7% per year for 2.5 years

You deposit $6215 into a bank account paying 7% simple interest per year. You left the money in for 4 years. How much interest do you get at the end of those 4 years?

Result

The interest is $1740.2.

Explanation

Find an interest by using the formula I=P⋅i⋅t, where I is interest, P is total principal, i is rate of interest per year, and t is total time in years.

In this examplee P = $6215, i = 7% and t = 4 years, so

III=P⋅i⋅t=6215⋅0.07⋅4=1740.2

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step-by-step explanation:

we have three similar triangles, because each has a right angle and shares an angle.   let's write the angles in order: opposite to short leg, long leg, hypotenuse.

cab similar to bad similar to cbd

or as ratios,

ca: ab: cb = ba: ad: bd = cb: bd: cd

we also know

ac = ad + cd

(ad+cd): ab: cb = ba: ad: bd = cb: bd: cd

(ad+cd)/cb=cb/cd

we have cb=6, ad=5 and seek x=cd.

we reject the negative root and conclude x=4

answer: 4