A timed set in the style of the numerical sections of consulting screening tests: twelve questions, 20 minutes, no calculator. The clock at the top counts down across the whole set and keeps running when you move between questions. These are our own questions, not any firm's test.
Pace yourself at about a minute and a half per question. If one stalls you, take your best estimate, note it on the scratch paper and move on; you can come back.