Should the buy commission be included in the initial investment when calculate the rate of return?

Just through the SS13, reading 52. On page 28 CFAI book. There is an example for an initial investment of 5,000 (on margin account). Especially from the errata, the rate of return was changed to: ($12,000-$5,000-$300-$200)/5,000 - 1 = 30% i.e. the buy commission $100 wasn’t included as initial investment. However, when I working on the problems for this reading (question 3 for example), the buy commission was included as part of the initial investment thus appeared in the denominotor. There is no clear definition in text what the initial investment is. Someone has an idea?

Hi, BlackDog. The February 5, 2008 version of the errata that is posted on the CFA Institute’s website for Level I addresses your inquiry. Hope this helps.

Thanks very much. That’s really helpful.