The number of times the "r" sound should be rolled in a word like "car" can vary depending on regional accents and individual speech patterns. In some accents, such as certain Scottish or Irish accents, the "r" sound may be rolled or trilled multiple times. However, in most standard English accents, including American, British, and Australian English, the "r" sound is typically not rolled or trilled but pronounced as a single sound.
In words like "car," the "r" sound is generally a single tap or approximate consonant sound, where the tongue quickly touches the alveolar ridge (the ridge just behind the upper teeth) before moving on to the next sound. So, in standard English, you would not typically roll or trill the "r" sound in words like "car."
It's important to note that accents and pronunciations can vary widely, and different dialects or regional variations may have different conventions for pronouncing certain sounds, including the "r" sound.