As it suggests, UPSC has included it in Aptitude Test to assess your mathematical and analytical skills.
Objective Test Techniques would be quite handy here as you may be having less time to solve the questions.
Learn to use ideas about basic numeracy skills, as well as practice questions based on number problems; number sequencing and data interpretation.
Locate, interpret, analyse and draw conclusions from data, taking into account data collection techniques.
Pick up useful tips to help you understand and answer questions without a calculator.