I just published video explanations to all of the 550 quantitative reasoning questions in the recently released 2021 Official GMAT Guide. There are a total of 42 new questions, 32 are Problem Solving and 10 are Data Sufficiency. The diagnostic test present in the 2020 Official GMAT Guide and earlier editions has been scrapped. The 48 quantitative reasoning questions in the diagnostic test have been moved to the online question bank that can be accessed at Wiley's efficient learning website.
https://gmatquantum.com/official-guides ... at-videos/