戴安（Diane）想为马拉松进行训练。她开始时在第一周跑了 1.6 km。之后每一周她都比前一周增加 1.2 km 的跑步距离。求她在前 5 周跑的总距离。 答：___ km

1. Calculate the running distance for each of the 5 weeks.

The distances for each week are:

• Week 1: $1.6\text{ km}$
• Week 2: $1.6 + 1.2 = 2.8\text{ km}$
• Week 3: $2.8 + 1.2 = 4.0\text{ km}$
• Week 4: $4.0 + 1.2 = 5.2\text{ km}$
• Week 5: $5.2 + 1.2 = 6.4\text{ km}$

2. Sum the weekly distances to find the total distance.

$\text{Total Distance} = 1.6 + 2.8 + 4.0 + 5.2 + 6.4$
$\text{Total Distance} = 20\text{ km}$