You can participate in whichever contest you want. (However, you can't register to both competitions.) The last two tasks in ABC are the same as the first two tasks in ARC.
ABC is significantly easier than Div2 contest in TopCoder or Codeforces. If you can enjoy Div2 contests in TC or CF, I recommend you to participate in ARC.
Time: August 6th (Sunday), 21:00 JST
・Duration: 100 minutes
・Number of Tasks: 4
・Rating： ARC is rated for those who have rating < 2800. ABC is rated for those who have rating < 1200. (However, note that current rating is much lower than your actual strength — if you are green or brown, I recommend you to choose ARC.)
The point values will be announced later.
We are looking forward to your participation!
Let's discuss after the contest.
The point values are announced.
It is 100 — 200 — 400 — 400 — 800 — 1200.