No specific preparation is required before taking the APT. The test is a measure of general academic skills (such as maths, literacy and problem solving) rather than learned knowledge, so no short term preparation will significantly impact performance. However, it may be beneficial for candidates to familiarise themselves with the style of questions that are used in this kind of assessment to ensure they feel comfortable on their test day.
There are numerous sample papers available online for CAT-style assessments online; a quick internet search will find some free resources. Search Reasoning Tests UK or CAT Samples.
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