Question 549804


{{{A=P(1+r/n)^(n*t)}}} Start with the compound interest formula



{{{4298.55=1987.22(1+r/12)^(12*15)}}} Plug in {{{A=4298.55}}}, {{{P=1987.22}}}, {{{n=12}}} and {{{t=15}}}.



{{{4298.55=1987.22(1+r/12)^(180)}}} Multiply {{{12}}} and {{{15}}} to get {{{180}}}.



{{{4298.55/1987.22=(1+r/12)^(180)}}} Divide both sides by {{{1987.22}}}.



{{{2.16309719105081=(1+r/12)^(180)}}} Evaluate {{{4298.55/1987.22}}} to get {{{2.16309719105081}}}.



{{{root(180,2.16309719105081)=1+r/12}}} Take the 180th root of both sides.



{{{1.00429553882184=1+r/12}}} Take the 180th root of {{{2.16309719105081}}} to get {{{1.00429553882184}}}.



{{{1.00429553882184-1=r/12}}} Subtract 1 from both sides.



{{{0.00429553882183731=r/12}}} Combine like terms.



{{{12*0.00429553882183731=r}}} Multiply boths sides by {{{12}}} to isolate "r".



{{{0.0515464658620477=r}}} Multiply {{{12}}} and {{{0.00429553882183731}}} to get {{{0.0515464658620477}}}.



{{{r=0.0515464658620477}}} Rearrange the equation.



{{{r=0.0515}}} Round to the nearest ten-thousandth.



So the interest rate is 5.15% (multiply by 100 to convert to a percentage)