Technically one should use quickly instead of fast. You don't run fast, you run quickly. You can, however, be a fast runner.
For the record, the word "fast," even without the -ly ending, can be used as an adverb. From a site called GrammarBook.com:
Rule 1. Many adverbs end in -ly, but many do not. Generally, if a word can have -ly added to its adjective form, place it there to form an adverb.
And then an example with "fast" is given:
She thinks fast/fastly. Fast answers the question how, so it is an adverb. But fast never has -ly attached to it.
Some recent examples from reputable publications:
"China's Pollution May Not Be Decreasing as Fast as Hoped"
A Scientific American headline
"For Slumping Mets, Summer Can't Come Fast Enough"
A Wall Street Journal headline
"Carbon is pouring into the atmosphere faster than at any time in the past 66 million years—since the dinosaurs went extinct—according to a new analysis of the geologic record."
A sentence in a National Geographic article
"If that’s you, some outlets may have some left, if you act fast."
A sentence in a Forbes article
Yes. Almost all adverbs end in "ly". Quickly, slowly, softly, noisily, loudly, heavily, haphazardly, awkwardly, drunkly, briskly, purposefully, randomly.
So I wrote "We walk quickly" and it counted it correct. But the translation is "We are running fast" Is laufen both walk and running? Or when is it considered which?
Yes, laufen either means walking or running. It's often used to say "going by foot" (as opposed to taking the car), but it can also mean a steady jogging speed (you laufen a marathon in German, since "rennen" would rather mean a sprint). What translation you use depends mostly on context.
Can anyone tell me why Laufen has no umlaut but Lauft does? Sorry I can't find the umlaut on my keyboard!
It's an irregular conjugation ;) Just one of those things you need to learn and accept
I took German in highschool (American) 45 years ago. This is very different. I learned walking was gehen, fahren was driving, rennen, running. Laufen is a new verb for me. Thank you for clarifying the the nuances between these words.
How can laufen mean two different forms of moving by foot? Is it like Aladeen in 'The Dictator', which meant both yes and no? Run! Don't walk, run!
I typed "we walked fast" and it said it was correct. I really don't know if that works...
Question about this one... Duo is giving me the answer as: We are running fast. Could you use, Wir rennen schnell instead?
I thought laufen was walking. There must be separate words for walking and running. Google translate uses rennen for running.