Word Problem, "investing over 5 years"?

Question

At the beginning of each year for 5 years, Cindy invests in a mutual fund with an average annual return of ‘r’.

The first year she invests $10, the second year $20, the third year $30, the forth year $40 and the fifth year $50.

If we assume that x = 1 + r, then at the end of the first year (just before next investment) the value is 10x dollars.

Because $20 is then added to the 10x dollars, the amount at the end of second year will be (10x + 20)x dollars and so on.

Find:

a) A polynomial in ‘x’ that represents the value of the investment at the end of the fifth year.

b) How much money will Cindy have after 5 years if r = 8%?

Answer 1

a) Value of investment=10 X5 + 20X4 + 30X3 + 40X2 + 50X

All numbers after X are supposed to be to the power

b) Just replace X by 1.08 and you get what you need