Melody invests $⁢50 in a stock fund. Each week, she adds an amount to the investment that is two times the previous week's addition. How much will Melody add to her investment in the 8th week? a_n=a_1⋅r^(n−1)

The weekly additions form a geometric sequence: the first addition is $50, and each week’s addition is twice the previous one. Using aₙ = a₁ · r⁽ⁿ⁻¹⁾, the 8th-week addition is $50 · 2⁷ = $6,400. Therefore, the correct choice is D, $6,400.

AI-written and checked against the verified answer.