Leaderboard writes many of the quant questions on the Greg Mat website, writes most of the solutions to said questions, and scored an official 170Q on the real test. The dude knows his math. If you're looking for some math help at an affordable cost, give a session with him a try.
Leaderboard is in the GMT+3 time zone.
If you have any questions, you can reach Leaderboard at leaderboard@gregmat.com.
