A free drill for the arithmetic consulting interviews and online tests demand: large numbers, percentages, ratios, fractions and growth rates, done in your head against the clock. Pick a mode, set a timer and a tolerance, and go. It runs in your browser and needs no account.
Case interviews are timed conversations. When the interviewer hands you a market of 68 million households and a 12% adoption rate, you are expected to reach about 8 million out loud, in seconds, while you keep the structure of the case in your head. A slow or wrong calculation costs more than the minute it takes: it breaks your train of thought, and interviewers read it as a sign of how you would handle numbers in front of a client.
The online screens are stricter still. The BCG Quant test asks for 20 typed numerical answers in 40 minutes without a calculator, and the McKinsey Solve games and Bain's SOVA numerical test all reward fast, accurate estimates. None of these tests is about advanced maths. They test the same handful of operations, done quickly and without slips.
A random mode mixes every type. Set the timer to 60 seconds, 2 or 5 minutes, or run a stopwatch, and choose how close an answer must be: an estimate within 10% is often what a case needs, while ratios and fraction conversions always need the exact answer.
Ten minutes a day beats an hour the night before. Start untimed until each type feels routine, then add the clock. Keep your zeros straight by writing figures in thousands, millions or billions rather than counting digits, and round early when the question allows it: 4.2 billion times 17% is close to 4.2 billion times a sixth, or 700 million.
When the drills feel easy, move on to calculations inside a case. Case Drills sets timed case maths with worked solutions, and the BCG Quant test guide covers the format of BCG's maths screen with worked practice questions. The BCG online test guide explains which test each BCG office sends.