Here's a slightly more risky, but easier way (my opinion) to get this achievement.
Set yourself up with 2 players that you can control. With each question, choose either 0% with one player, and "higher" with the other.
In round 2, it's a little more strategic; you'll want to get a feel for whether you think the answer is greater or less than 50% and choose either 100% or 0% each time so that the other player can pick "much higher" or "much lower" and be 50% away from it.
Example: how many people have televisions in their bedrooms? I figured it was more than 50%, so I chose 0% as the player, and then picked "much higher" with the other. The answer was 63% or something, but hopefully you get the idea. Just keep doing this until you get to the 3rd round, and as long as you've been correct in the much higher/lower each time, you're safe. Since you're playing as both characters (ideally under a single xbox gamertag), you have a safety net in case you miss an answer with one character, you still have the other.
I got this the first time I tried it this way.