If I was or If I were

Why is was used in the first sentence and were in the second?

If I were a millionaire, I would buy a yacht.
If I was late, it was because I got stuck in traffic.

Were for unreal situations

Use were when talking about imagined, hypothetical situations.

If I were you, I would book a flight now.
If you were an animal, you would be a cat!
I would ask her out on a date if I were ten years younger!

Was for real situations

Use was when talking about real situations that happened in the past.

If I was looking tired, it was because I hadn't had much sleep.
If I was smoking inside, it was because it was raining.
If didn't say 'hello', it was because I didn't see you.

Now decide if these sentences should use were or was:

• 1) If you ___ invisible, what would you do?
  
  was
  were
  
  
• 2) If I ___ braver, I would go skydiving.
  
  was
  were
  
  
• 3) If she ___ singing, she was in a good mood.
  
  were
  was
  
  
• 4) If I __ her, I would study harder.
  
  was
  were
  
  
• 5) If I ___ on my bike, it was the weekend.
  
  were
  was
  
  
• 6) If I ___ answering my phone, I was in a meeting.
  
  wasn't
  weren't
  
  
• 7) If he ___ faster, he could have been a professional footballer.
  
  was
  were