I know this post is old, but I just want to make a quick point here. The Economist is a great publication, and I enjoy reading it every week. That said, it is written using British grammar rules. The GMAT, on the other hand, uses standard American rules.
One example:
Correct in British publications: "The army have captured the enemy leader."
Correct on the GMAT: "The army has captured the enemy leader."
This is one of many minor differences between the two grammatical systems, but collectively the differences would lead me to suggest practicing for the GMAT by reading U.S. publications.
Best of luck!