GMAT - Quant

I just gave a diagnostics test for GMAT. As it turns out my quantitative is weak. I found quite a few posts on improving SC, CR, AWA etc. Any suggestions for improving quant? I need to review basics and need practice test.

I just gave a diagnostics test for GMAT. As it turns out my quantitative is weak. I found quite a few posts on improving SC, CR, AWA etc. Any suggestions for improving quant? I need to review basics and need practice test.

Where can I find a simple pdf with quant concepts explained? DS and PS.