How long will the Sun have spent as a main-sequence star when it finally begins to evolve toward the red giant phase?

Question

Quizplus · Accepted Answer

The Sun is currently about 4.6 billion years old and is expected to become a red giant in another 5 billion years or so. Therefore, it will have spent approximately 10 billion years as a main-sequence star before evolving toward the red giant phase, which is option D.

How Long Will the Sun Have Spent as a Main-Sequence