First let's figure out how many meters she ran. She ran 650 meters out of each kilometer, so she ran (650m)*2 = 1300m (since the race was 2km).
The question asks for the distance she ran in kilometers, so we need to convert 1300m to km.
There are 1000m in 1 km, so the conversion factor is [tex] \frac{1000m}{1km} [/tex] or [tex] \frac{1km}{1000m} [/tex].
We can use dimensional analysis to easily convert. This is simply multiplying the original number and unit by the conversion factor (since the conversion factor simplifies to 1, it will only change the unit and not the value).
Make sure the unit of the original number, the one you want to convert, is in the denominator of the conversion factor so that the original unit cancels to become the new unit (which is in the numerator).
In this case, we use [tex] \frac{1km}{1000m} [/tex] because to denominator with m will cancel with the meters from the original unit.
[tex] \frac{1300m}{1} * \frac{1km}{1000m} = \frac{1300km}{1000} = 1.3km[/tex]
