That’s an excellent question
and while I don’t think there is one magical ratio, making sure to constantly review concepts you’ve learned will prevent them from atrophying.
Your current approach – studying a specific concept and tackling all the OG problems pertaining to that concept may result in a tunnel vision. However, I wouldn’t throw the baby out with the bathwater.
Become confident in an area, say percents, by making sure you can finish medium-level questions in < 2 minutes (you don’t necessarily have to go through every single problem in the guide the first time around).
Then move on to a different concept, say exponents, but make sure to come back to percents a couple of times a week during your study time.
Of course concepts will start piling on, but the hope is by revisiting concepts after they’ve incubated for a little while, you will need to spend less on them each time.
Also by varying up the problems you expose yourself to during your study sessions you will mirror the structure of the actual test.
Speaking of which - it is also important to do random problem sets whenever you can. That is you want to wean yourself off of a predictable problem set – you need to be ready for test day. By re-exposing yourself in this manner to problems across the board you can also determine which areas need more work and which ones you can spend less time on.
For problem sets, I would recommend doing ten random problems at a time, varying difficulty. Perhaps you can do them every other day, leaving you enough time to focus on a concept.
Hopefully, by making your study approach more dynamic you will be able to adapt to the dynamic – and very challenging – test that is the GMAT.
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