I have been getting around 65 to 70 % in the Rita Mulachy fast track exams

Scordo around 78 to 82 % 

PM Study got 70% today 

I found Scordo and PMStudy quite close, PMStudy is slightly on the tougher side. 

But Rita I am finding way difficult. Is the actual exam that tough ? Should I try giving more of Rita exams  ? Or should I switch to HF and Oliver Lehman exams  ?