Fruit Ninja

It is possible to get a score of over 400 without any powerups, but you will make life a lot easier for yourself by buying as many as you can of everything. Stock up on Bombs, Peaches and Berry Blasts, and go for big combos. This will pop at the results screen after all bonuses are calculated.
Unfortunately, at the moment Arcade mode is glitched, and the game will freeze/close before the bonuses are added on. Until this is fixed use the following steps:
You only need to do these steps if the game freezes at the end of Arcade Mode every time.

1. Load up Fruit Ninja
2. Go to the desktop and switch the date backwards (I used September 1st)
3. Go back to Fruit Ninja and you should see a message that says "disconnected from xbox live"
4. Play with this "offline" profile and obtain the arcade mode achievement
5. Once you see it unlock for the offline profile switch back to the desktop and sync your pc time with the internet
6. Go back to Fruit Ninja and press the sign in button
7. Once you sign in check your achievements once (don't know if this forced xbox.com to update but the first time I checked the achievement was not unlocked)
8. Go to xbox.com and hopefully the achievement has been updated

Thanks to DarkxMaterials for this solution.