Since 'Kemach' is coarse flour and 'So'les', fine wheat-flour, how will we explain the apparent contradiction?
Rashi: The 'So'les' was in order to prepare cakes, and the 'Kemach' to draw the scum from the pot.
Ramban: He took three Sa'ah of Kemach, which he ground a number of times until he had sufficient fine flour to make bread for his guests.
Hadar Zekenim, based on Bava Metzi'a 87a: First, he said "Kemach" (he thought that it is obvious that he intends for So'les). Sarah asked if she should use coarse flour, so he needed to explicitly say So'les. 1
Bava Metzi'a (Ibid.): From here we see that women tend to be more stingy with guests than men.
Why did Avraham tell Sarah to hurry?
Hadar Zekenim: Became women tend to be lazy.