Don't understand how dollar weighted return was found

. Arithmetic average return = 10%+25%+(-20%)+20% = 8.75% . Geometric average return R satisfies: 4 (1 + R)4= (1 + 10%) x (1 + 25%) x (1 - 20%) x (1 + 20%) R = [(1 + 10%) x (1 + 25%) x (1 - 20%) x (1 + 20%)]1/4-1 = 7.19% . To calculate the dollar weighted return, treat the mutual fund as a project that takes cash flow in and generates cash flow out. The cash flow diagram is as follows: -0.1 -0,5 0.8 -0.6 + 1.56 = 0.96 0 1 2 3 4 Then by the definition of IRR: 0 =-1+ -0.1 -0.5 0.8 0.96 1 + IRR (1 + IRR) 2 (1 + IRR) 3 (1 + IRR) 4 IRR = 3.38% 9