This isn't a stock index as much as it is a portfolio, but it doesn't matter.
On day one the assets are worth
8000*4.25+5000*2.90+2000*6.40 = $61,300
On day 8
8000*3.90 + 5000*2.50 + 2000*6.10 = $55,900
Change: 55900/61300 - 1 = -.08809
That seems like none of the above but we'll choose
choice B
