A good stockdash–based mutual fund should earn at least 55% per year over a long period of time. Consider the case of Barney and Lynn, who were overheard gloating (for all to hear) about how well they had done with their mutual fund investment." We turned a $25 comma 00025,000 investment of money in 19821982 into $100 comma 000100,000 in 20072007."

5.70%

Step-by-step explanation:

Correct word "We turned a $25,000 investment of money in 1982 into $100,000 in 2007."  What return (interest rate) did they really earn on their investment?

No of years(1982 to 2007) = 25 years

The average annual return is R%, so $25,000 * (1 + R)^25 = $100,000

(1 + R)^25 = $100,000 / $25,000

(1 + R)^25 = 4

We take 25th root on each side

(1 + R)^(25*1/25) =

1 + R = 1.0570

R = 1.0570 - 1

R = 0.057

R = 5.70%

So, the return (interest rate) they really earn on their investment is 5.70%.