Answer :
Given :
When Colby was born, his parents invested $1,000 in a fund that paid an
annual interest of 8%.
To Find :
How old will Colby be when the investment is worth at least $4,000 .
Solution :
Let, time taken is x years.
So, the formula is :
[tex]P = A_o + \dfrac{A_o \times r\times t}{100}\\\\4000 = 1000 + \dfrac{1000\times 8\times t}{100} \\\\80t = 3000\\\\t = \dfrac{3000}{80} \ years\\\\t = 37.5\ years[/tex]
Therefore, Colby will be 37.5 years old.
The age of Colby will be [tex]37.5[/tex] years.
Simple interest :
The amount after t years is given by,
[tex]A=P+(\frac{P*r*t}{100} )[/tex]
Where P is principal, r is rate and t is time in years.
Given that, [tex]A=4000,P=1000,r=8\%[/tex]
Substitute values in above equations.
[tex]4000=1000+\frac{1000*8*t}{100} \\\\\frac{1000*8*t}{100}=3000\\\\t=37.5years[/tex]
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